Add IAM Auth Method (#12583)

This adds an aws-iam auth method type which supports authenticating to Consul using AWS IAM identities.

Co-authored-by: R.B. Boyer <4903+rboyer@users.noreply.github.com>

.changelog/12583.txt

@@ -0,0 +1,3 @@
+```release-note:feature
+acl: Added an AWS IAM auth method that allows authenticating to Consul using AWS IAM identities
+```

agent/consul/acl_authmethod.go

@@ -8,6 +8,7 @@ import (
 	"github.com/hashicorp/go-bexpr"
 
 	// register these as a builtin auth method
+	_ "github.com/hashicorp/consul/agent/consul/authmethod/awsauth"
 	_ "github.com/hashicorp/consul/agent/consul/authmethod/kubeauth"
 	_ "github.com/hashicorp/consul/agent/consul/authmethod/ssoauth"
 )

agent/consul/authmethod/awsauth/aws.go

@@ -0,0 +1,193 @@
+package awsauth
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/hashicorp/consul/agent/consul/authmethod"
+	"github.com/hashicorp/consul/agent/structs"
+	"github.com/hashicorp/consul/internal/iamauth"
+	"github.com/hashicorp/go-hclog"
+)
+
+const (
+	authMethodType string = "aws-iam"
+
+	IAMServerIDHeaderName  string = "X-Consul-IAM-ServerID"
+	GetEntityMethodHeader  string = "X-Consul-IAM-GetEntity-Method"
+	GetEntityURLHeader     string = "X-Consul-IAM-GetEntity-URL"
+	GetEntityHeadersHeader string = "X-Consul-IAM-GetEntity-Headers"
+	GetEntityBodyHeader    string = "X-Consul-IAM-GetEntity-Body"
+)
+
+func init() {
+	// register this as an available auth method type
+	authmethod.Register(authMethodType, func(logger hclog.Logger, method *structs.ACLAuthMethod) (authmethod.Validator, error) {
+		v, err := NewValidator(logger, method)
+		if err != nil {
+			return nil, err
+		}
+		return v, nil
+	})
+}
+
+type Config struct {
+	// BoundIAMPrincipalARNs are the trusted AWS IAM principal ARNs that are permitted
+	// to login to the auth method. These can be the exact ARNs or wildcards. Wildcards
+	// are only supported if EnableIAMEntityDetails is true.
+	BoundIAMPrincipalARNs []string `json:",omitempty"`
+
+	// EnableIAMEntityDetails will fetch the IAM User or IAM Role details to include
+	// in binding rules. Required if wildcard principal ARNs are used.
+	EnableIAMEntityDetails bool `json:",omitempty"`
+
+	// IAMEntityTags are the specific IAM User or IAM Role tags to include as selectable
+	// fields in the binding rule attributes. Requires EnableIAMEntityDetails = true.
+	IAMEntityTags []string `json:",omitempty"`
+
+	// ServerIDHeaderValue adds a X-Consul-IAM-ServerID header to each AWS API request.
+	// This helps protect against replay attacks.
+	ServerIDHeaderValue string `json:",omitempty"`
+
+	// MaxRetries is the maximum number of retries on AWS API requests for recoverable errors.
+	MaxRetries int `json:",omitempty"`
+	// IAMEndpoint is the AWS IAM endpoint where iam:GetRole or iam:GetUser requests will be sent.
+	// Note that the Host header in a signed request cannot be changed.
+	IAMEndpoint string `json:",omitempty"`
+	// STSEndpoint is the AWS STS endpoint where sts:GetCallerIdentity requests will be sent.
+	// Note that the Host header in a signed request cannot be changed.
+	STSEndpoint string `json:",omitempty"`
+	// STSRegion is the region for the AWS STS service. This should only be set if STSEndpoint
+	// is set, and must match the region of the STSEndpoint.
+	STSRegion string `json:",omitempty"`
+
+	// AllowedSTSHeaderValues is a list of additional allowed headers on the sts:GetCallerIdentity
+	// request in the bearer token. A default list of necessary headers is allowed in any case.
+	AllowedSTSHeaderValues []string `json:",omitempty"`
+}
+
+func (c *Config) convertForLibrary() *iamauth.Config {
+	return &iamauth.Config{
+		BoundIAMPrincipalARNs:  c.BoundIAMPrincipalARNs,
+		EnableIAMEntityDetails: c.EnableIAMEntityDetails,
+		IAMEntityTags:          c.IAMEntityTags,
+		ServerIDHeaderValue:    c.ServerIDHeaderValue,
+		MaxRetries:             c.MaxRetries,
+		IAMEndpoint:            c.IAMEndpoint,
+		STSEndpoint:            c.STSEndpoint,
+		STSRegion:              c.STSRegion,
+		AllowedSTSHeaderValues: c.AllowedSTSHeaderValues,
+
+		ServerIDHeaderName:     IAMServerIDHeaderName,
+		GetEntityMethodHeader:  GetEntityMethodHeader,
+		GetEntityURLHeader:     GetEntityURLHeader,
+		GetEntityHeadersHeader: GetEntityHeadersHeader,
+		GetEntityBodyHeader:    GetEntityBodyHeader,
+	}
+}
+
+type Validator struct {
+	name   string
+	config *iamauth.Config
+	logger hclog.Logger
+
+	auth *iamauth.Authenticator
+}
+
+func NewValidator(logger hclog.Logger, method *structs.ACLAuthMethod) (*Validator, error) {
+	if method.Type != authMethodType {
+		return nil, fmt.Errorf("%q is not an AWS IAM auth method", method.Name)
+	}
+
+	var config Config
+	if err := authmethod.ParseConfig(method.Config, &config); err != nil {
+		return nil, err
+	}
+	iamConfig := config.convertForLibrary()
+
+	auth, err := iamauth.NewAuthenticator(iamConfig, logger)
+	if err != nil {
+		return nil, err
+	}
+
+	return &Validator{
+		name:   method.Name,
+		config: iamConfig,
+		logger: logger,
+		auth:   auth,
+	}, nil
+}
+
+// Name implements authmethod.Validator.
+func (v *Validator) Name() string { return v.name }
+
+// Stop implements authmethod.Validator.
+func (v *Validator) Stop() {}
+
+// ValidateLogin implements authmethod.Validator.
+func (v *Validator) ValidateLogin(ctx context.Context, loginToken string) (*authmethod.Identity, error) {
+	details, err := v.auth.ValidateLogin(ctx, loginToken)
+	if err != nil {
+		return nil, err
+	}
+
+	vars := map[string]string{
+		"entity_name": details.EntityName,
+		"entity_id":   details.EntityId,
+		"account_id":  details.AccountId,
+	}
+	fields := &awsSelectableFields{
+		EntityName: details.EntityName,
+		EntityId:   details.EntityId,
+		AccountId:  details.AccountId,
+	}
+
+	if v.config.EnableIAMEntityDetails {
+		vars["entity_path"] = details.EntityPath
+		fields.EntityPath = details.EntityPath
+		fields.EntityTags = map[string]string{}
+		for _, tag := range v.config.IAMEntityTags {
+			vars["entity_tags."+tag] = details.EntityTags[tag]
+			fields.EntityTags[tag] = details.EntityTags[tag]
+		}
+	}
+
+	result := &authmethod.Identity{
+		SelectableFields: fields,
+		ProjectedVars:    vars,
+		EnterpriseMeta:   nil,
+	}
+	return result, nil
+
+}
+
+func (v *Validator) NewIdentity() *authmethod.Identity {
+	fields := &awsSelectableFields{
+		EntityTags: map[string]string{},
+	}
+	vars := map[string]string{
+		"entity_name": "",
+		"entity_id":   "",
+		"account_id":  "",
+	}
+	if v.config.EnableIAMEntityDetails {
+		vars["entity_path"] = ""
+		for _, tag := range v.config.IAMEntityTags {
+			vars["entity_tags."+tag] = ""
+			fields.EntityTags[tag] = ""
+		}
+	}
+	return &authmethod.Identity{
+		SelectableFields: fields,
+		ProjectedVars:    vars,
+	}
+}
+
+type awsSelectableFields struct {
+	EntityName string `bexpr:"entity_name"`
+	EntityId   string `bexpr:"entity_id"`
+	AccountId  string `bexpr:"account_id"`
+
+	EntityPath string            `bexpr:"entity_path"`
+	EntityTags map[string]string `bexpr:"entity_tags"`
+}

agent/consul/authmethod/awsauth/aws_test.go

@@ -0,0 +1,342 @@
+package awsauth
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/aws/aws-sdk-go/aws/credentials"
+	"github.com/hashicorp/consul/agent/consul/authmethod"
+	"github.com/hashicorp/consul/agent/structs"
+	"github.com/hashicorp/consul/internal/iamauth"
+	"github.com/hashicorp/consul/internal/iamauth/iamauthtest"
+	"github.com/hashicorp/go-hclog"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewValidator(t *testing.T) {
+	f := iamauthtest.MakeFixture()
+	expConfig := &iamauth.Config{
+		BoundIAMPrincipalARNs:  []string{f.AssumedRoleARN},
+		EnableIAMEntityDetails: true,
+		IAMEntityTags:          []string{"tag-1"},
+		ServerIDHeaderValue:    "x-some-header",
+		MaxRetries:             3,
+		IAMEndpoint:            "iam-endpoint",
+		STSEndpoint:            "sts-endpoint",
+		STSRegion:              "sts-region",
+		AllowedSTSHeaderValues: []string{"header-value"},
+		ServerIDHeaderName:     "X-Consul-IAM-ServerID",
+		GetEntityMethodHeader:  "X-Consul-IAM-GetEntity-Method",
+		GetEntityURLHeader:     "X-Consul-IAM-GetEntity-URL",
+		GetEntityHeadersHeader: "X-Consul-IAM-GetEntity-Headers",
+		GetEntityBodyHeader:    "X-Consul-IAM-GetEntity-Body",
+	}
+
+	type AM = *structs.ACLAuthMethod
+	// Create the auth method, with an optional modification function.
+	makeMethod := func(modifyFn func(AM)) AM {
+		config := map[string]interface{}{
+			"BoundIAMPrincipalARNs":  []string{f.AssumedRoleARN},
+			"EnableIAMEntityDetails": true,
+			"IAMEntityTags":          []string{"tag-1"},
+			"ServerIDHeaderValue":    "x-some-header",
+			"MaxRetries":             3,
+			"IAMEndpoint":            "iam-endpoint",
+			"STSEndpoint":            "sts-endpoint",
+			"STSRegion":              "sts-region",
+			"AllowedSTSHeaderValues": []string{"header-value"},
+		}
+
+		m := &structs.ACLAuthMethod{
+			Name:        "test-iam",
+			Type:        "aws-iam",
+			Description: "aws iam auth",
+			Config:      config,
+		}
+		if modifyFn != nil {
+			modifyFn(m)
+		}
+		return m
+	}
+
+	cases := map[string]struct {
+		ok       bool
+		modifyFn func(AM)
+	}{
+		"success":                  {true, nil},
+		"wrong type":               {false, func(m AM) { m.Type = "not-iam" }},
+		"extra config":             {false, func(m AM) { m.Config["extraField"] = "123" }},
+		"wrong config value type":  {false, func(m AM) { m.Config["MaxRetries"] = []string{"1"} }},
+		"missing bound principals": {false, func(m AM) { delete(m.Config, "BoundIAMPrincipalARNs") }},
+	}
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			v, err := NewValidator(nil, makeMethod(c.modifyFn))
+			if c.ok {
+				require.NoError(t, err)
+				require.NotNil(t, v)
+				require.Equal(t, "test-iam", v.name)
+				require.NotNil(t, v.auth)
+				require.Equal(t, expConfig, v.config)
+			} else {
+				require.Error(t, err)
+				require.Nil(t, v)
+			}
+		})
+	}
+}
+
+func TestValidateLogin(t *testing.T) {
+	f := iamauthtest.MakeFixture()
+
+	cases := map[string]struct {
+		server    *iamauthtest.Server
+		token     string
+		config    map[string]interface{}
+		expVars   map[string]string
+		expFields []string
+		expError  string
+	}{
+		"success - role login": {
+			server: f.ServerForRole,
+			config: map[string]interface{}{
+				"BoundIAMPrincipalARNs": []string{f.CanonicalRoleARN},
+			},
+			expVars: map[string]string{
+				"entity_id":   f.EntityID,
+				"entity_name": f.RoleName,
+				"account_id":  f.AccountID,
+			},
+			expFields: []string{
+				fmt.Sprintf(`entity_id == %q`, f.EntityID),
+				fmt.Sprintf(`entity_name == %q`, f.RoleName),
+				fmt.Sprintf(`account_id == %q`, f.AccountID),
+			},
+		},
+		"success - user login": {
+			server: f.ServerForUser,
+			config: map[string]interface{}{
+				"BoundIAMPrincipalARNs": []string{f.UserARN},
+			},
+			expVars: map[string]string{
+				"entity_id":   f.EntityID,
+				"entity_name": f.UserName,
+				"account_id":  f.AccountID,
+			},
+			expFields: []string{
+				fmt.Sprintf(`entity_id == %q`, f.EntityID),
+				fmt.Sprintf(`entity_name == %q`, f.UserName),
+				fmt.Sprintf(`account_id == %q`, f.AccountID),
+			},
+		},
+		"success - role login with entity details": {
+			server: f.ServerForUser,
+			config: map[string]interface{}{
+				"BoundIAMPrincipalARNs":  []string{f.UserARN},
+				"EnableIAMEntityDetails": true,
+			},
+			expVars: map[string]string{
+				"entity_id":   f.EntityID,
+				"entity_name": f.UserName,
+				"account_id":  f.AccountID,
+				"entity_path": f.UserPath,
+			},
+			expFields: []string{
+				fmt.Sprintf(`entity_id == %q`, f.EntityID),
+				fmt.Sprintf(`entity_name == %q`, f.UserName),
+				fmt.Sprintf(`account_id == %q`, f.AccountID),
+				fmt.Sprintf(`entity_path == %q`, f.UserPath),
+			},
+		},
+		"success - user login with entity details": {
+			server: f.ServerForUser,
+			config: map[string]interface{}{
+				"BoundIAMPrincipalARNs":  []string{f.UserARN},
+				"EnableIAMEntityDetails": true,
+			},
+			expVars: map[string]string{
+				"entity_id":   f.EntityID,
+				"entity_name": f.UserName,
+				"account_id":  f.AccountID,
+				"entity_path": f.UserPath,
+			},
+			expFields: []string{
+				fmt.Sprintf(`entity_id == %q`, f.EntityID),
+				fmt.Sprintf(`entity_name == %q`, f.UserName),
+				fmt.Sprintf(`account_id == %q`, f.AccountID),
+				fmt.Sprintf(`entity_path == %q`, f.UserPath),
+			},
+		},
+		"invalid token": {
+			server: f.ServerForUser,
+			config: map[string]interface{}{
+				"BoundIAMPrincipalARNs": []string{f.UserARN},
+			},
+			token:    `invalid`,
+			expError: "invalid token",
+		},
+		"empty json token": {
+			server: f.ServerForUser,
+			config: map[string]interface{}{
+				"BoundIAMPrincipalARNs": []string{f.UserARN},
+			},
+			token:    `{}`,
+			expError: "invalid token",
+		},
+		"empty json fields in token": {
+			server: f.ServerForUser,
+			config: map[string]interface{}{
+				"BoundIAMPrincipalARNs": []string{f.UserARN},
+			},
+			token: `{"iam_http_request_method": "",
+"iam_request_body": "",
+"iam_request_headers": "",
+"iam_request_url": ""
+}`,
+			expError: "invalid token",
+		},
+	}
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			v, _, token := setup(t, c.config, c.server)
+			if c.token != "" {
+				token = c.token
+			}
+			id, err := v.ValidateLogin(context.Background(), token)
+			if c.expError != "" {
+				require.Error(t, err)
+				require.Contains(t, err.Error(), c.expError)
+				require.Nil(t, id)
+			} else {
+				require.NoError(t, err)
+				authmethod.RequireIdentityMatch(t, id, c.expVars, c.expFields...)
+			}
+		})
+	}
+}
+
+func setup(t *testing.T, config map[string]interface{}, server *iamauthtest.Server) (*Validator, *httptest.Server, string) {
+	t.Helper()
+
+	fakeAws := iamauthtest.NewTestServer(t, server)
+
+	config["STSEndpoint"] = fakeAws.URL + "/sts"
+	config["STSRegion"] = "fake-region"
+	config["IAMEndpoint"] = fakeAws.URL + "/iam"
+
+	method := &structs.ACLAuthMethod{
+		Name:   "test-method",
+		Type:   "aws-iam",
+		Config: config,
+	}
+	nullLogger := hclog.NewNullLogger()
+	v, err := NewValidator(nullLogger, method)
+	require.NoError(t, err)
+
+	// Generate the login token
+	tokenData, err := iamauth.GenerateLoginData(&iamauth.LoginInput{
+		Creds:                  credentials.NewStaticCredentials("fake", "fake", ""),
+		IncludeIAMEntity:       v.config.EnableIAMEntityDetails,
+		STSEndpoint:            v.config.STSEndpoint,
+		STSRegion:              v.config.STSRegion,
+		Logger:                 nullLogger,
+		ServerIDHeaderValue:    v.config.ServerIDHeaderValue,
+		ServerIDHeaderName:     v.config.ServerIDHeaderName,
+		GetEntityMethodHeader:  v.config.GetEntityMethodHeader,
+		GetEntityURLHeader:     v.config.GetEntityURLHeader,
+		GetEntityHeadersHeader: v.config.GetEntityHeadersHeader,
+		GetEntityBodyHeader:    v.config.GetEntityBodyHeader,
+	})
+	require.NoError(t, err)
+
+	token, err := json.Marshal(tokenData)
+	require.NoError(t, err)
+	return v, fakeAws, string(token)
+}
+
+func TestNewIdentity(t *testing.T) {
+	principals := []string{"arn:aws:sts::1234567890:assumed-role/my-role/some-session"}
+	cases := map[string]struct {
+		config     map[string]interface{}
+		expVars    map[string]string
+		expFilters []string
+	}{
+		"entity details disabled": {
+			config: map[string]interface{}{
+				"BoundIAMPrincipalARNs": principals,
+			},
+			expVars: map[string]string{
+				"entity_name": "",
+				"entity_id":   "",
+				"account_id":  "",
+			},
+			expFilters: []string{
+				`entity_name == ""`,
+				`entity_id == ""`,
+				`account_id == ""`,
+			},
+		},
+		"entity details enabled": {
+			config: map[string]interface{}{
+				"BoundIAMPrincipalARNs":  principals,
+				"EnableIAMEntityDetails": true,
+			},
+			expVars: map[string]string{
+				"entity_name": "",
+				"entity_id":   "",
+				"account_id":  "",
+				"entity_path": "",
+			},
+			expFilters: []string{
+				`entity_name == ""`,
+				`entity_id == ""`,
+				`account_id == ""`,
+				`entity_path == ""`,
+			},
+		},
+		"entity tags": {
+			config: map[string]interface{}{
+				"BoundIAMPrincipalARNs":  principals,
+				"EnableIAMEntityDetails": true,
+				"IAMEntityTags": []string{
+					"test_tag",
+					"test_tag_2",
+				},
+			},
+			expVars: map[string]string{
+				"entity_name":            "",
+				"entity_id":              "",
+				"account_id":             "",
+				"entity_path":            "",
+				"entity_tags.test_tag":   "",
+				"entity_tags.test_tag_2": "",
+			},
+			expFilters: []string{
+				`entity_name == ""`,
+				`entity_id == ""`,
+				`account_id == ""`,
+				`entity_path == ""`,
+				`entity_tags.test_tag == ""`,
+				`entity_tags.test_tag_2 == ""`,
+			},
+		},
+	}
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			method := &structs.ACLAuthMethod{
+				Name:   "test-method",
+				Type:   "aws-iam",
+				Config: c.config,
+			}
+			nullLogger := hclog.NewNullLogger()
+			v, err := NewValidator(nullLogger, method)
+			require.NoError(t, err)
+
+			id := v.NewIdentity()
+			authmethod.RequireIdentityMatch(t, id, c.expVars, c.expFilters...)
+		})
+	}
+}

command/login/aws.go

@@ -0,0 +1,148 @@
+package login
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+
+	"github.com/aws/aws-sdk-go/aws"
+	"github.com/aws/aws-sdk-go/aws/credentials"
+	"github.com/aws/aws-sdk-go/aws/session"
+
+	"github.com/hashicorp/consul/agent/consul/authmethod/awsauth"
+	"github.com/hashicorp/consul/internal/iamauth"
+	"github.com/hashicorp/go-hclog"
+)
+
+type AWSLogin struct {
+	autoBearerToken     bool
+	includeEntity       bool
+	stsEndpoint         string
+	region              string
+	serverIDHeaderValue string
+	accessKeyId         string
+	secretAccessKey     string
+	sessionToken        string
+}
+
+func (a *AWSLogin) flags() *flag.FlagSet {
+	fs := flag.NewFlagSet("", flag.ContinueOnError)
+	fs.BoolVar(&a.autoBearerToken, "aws-auto-bearer-token", false,
+		"Construct a bearer token and login to the AWS IAM auth method. This requires AWS credentials. "+
+			"AWS credentials are automatically discovered from standard sources supported by the Go SDK for "+
+			"AWS. Alternatively, explicit credentials can be passed using the -aws-acesss-key-id and "+
+			"-aws-secret-access-key flags. [aws-iam only]")
+
+	fs.BoolVar(&a.includeEntity, "aws-include-entity", false,
+		"Include a signed request to get the IAM role or IAM user in the bearer token. [aws-iam only]")
+
+	fs.StringVar(&a.stsEndpoint, "aws-sts-endpoint", "",
+		"URL for AWS STS API calls. [aws-iam only]")
+
+	fs.StringVar(&a.region, "aws-region", "",
+		"Region for AWS API calls. If set, should match the region of -aws-sts-endpoint. "+
+			"If not provided, the region will be discovered from standard sources, such as "+
+			"the AWS_REGION environment variable. [aws-iam only]")
+
+	fs.StringVar(&a.serverIDHeaderValue, "aws-server-id-header-value", "",
+		"If set, an X-Consul-IAM-ServerID header is included in signed AWS API request(s) that form "+
+			"the bearer token. This value must match the server-side configured value for the auth method "+
+			"in order to login. This is optional and helps protect against replay attacks. [aws-iam only]")
+
+	fs.StringVar(&a.accessKeyId, "aws-access-key-id", "",
+		"AWS access key id to use. Requires -aws-secret-access-key if specified. [aws-iam only]")
+
+	fs.StringVar(&a.secretAccessKey, "aws-secret-access-key", "",
+		"AWS secret access key to use. Requires -aws-access-key-id if specified. [aws-iam only]")
+
+	fs.StringVar(&a.sessionToken, "aws-session-token", "",
+		"AWS session token to use. Requires -aws-access-key-id and -aws-secret-access-key if "+
+			"specified. [aws-iam only]")
+	return fs
+}
+
+// checkFlags validates flags for the aws-iam auth method.
+func (a *AWSLogin) checkFlags() error {
+	if !a.autoBearerToken {
+		if a.includeEntity || a.stsEndpoint != "" || a.region != "" || a.serverIDHeaderValue != "" ||
+			a.accessKeyId != "" || a.secretAccessKey != "" || a.sessionToken != "" {
+			return fmt.Errorf("Missing '-aws-auto-bearer-token' flag")
+		}
+	}
+	if a.accessKeyId != "" && a.secretAccessKey == "" {
+		return fmt.Errorf("Missing '-aws-secret-access-key' flag")
+	}
+	if a.secretAccessKey != "" && a.accessKeyId == "" {
+		return fmt.Errorf("Missing '-aws-access-key-id' flag")
+	}
+	if a.sessionToken != "" && (a.accessKeyId == "" || a.secretAccessKey == "") {
+		return fmt.Errorf("Missing '-aws-access-key-id' and '-aws-secret-access-key' flags")
+	}
+	return nil
+}
+
+// createAWSBearerToken generates a bearer token string for the AWS IAM auth method.
+// It will discover AWS credentials which are used to sign AWS API requests.
+// Alternatively, static credentials can be passed as flags.
+//
+// The bearer token contains a signed sts:GetCallerIdentity request.
+// If aws-include-entity is specified, a signed iam:GetRole or iam:GetUser request is
+// also included. The AWS credentials are used to retrieve the current user's role
+// or user name for the iam:GetRole or iam:GetUser request.
+func (a *AWSLogin) createAWSBearerToken() (string, error) {
+	cfg := aws.Config{
+		Endpoint: aws.String(a.stsEndpoint),
+		Region:   aws.String(a.region),
+		// More detailed error message to help debug credential discovery.
+		CredentialsChainVerboseErrors: aws.Bool(true),
+	}
+
+	if a.accessKeyId != "" {
+		// Use creds from flags.
+		cfg.Credentials = credentials.NewStaticCredentials(
+			a.accessKeyId, a.secretAccessKey, a.sessionToken,
+		)
+	}
+
+	// Session loads creds from standard sources (env vars, file, EC2 metadata, ...)
+	sess, err := session.NewSessionWithOptions(session.Options{
+		Config: cfg,
+		// Allow loading from config files by default:
+		//   ~/.aws/config or AWS_CONFIG_FILE
+		//   ~/.aws/credentials or AWS_SHARED_CREDENTIALS_FILE
+		SharedConfigState: session.SharedConfigEnable,
+	})
+	if err != nil {
+		return "", err
+	}
+	if sess.Config.Region == nil || *sess.Config.Region == "" {
+		return "", fmt.Errorf("AWS region not found")
+	}
+	if sess.Config.Credentials == nil {
+		return "", fmt.Errorf("AWS credentials not found")
+	}
+	creds := sess.Config.Credentials
+
+	loginData, err := iamauth.GenerateLoginData(&iamauth.LoginInput{
+		Creds:                  creds,
+		IncludeIAMEntity:       a.includeEntity,
+		STSEndpoint:            a.stsEndpoint,
+		STSRegion:              a.region,
+		Logger:                 hclog.New(nil),
+		ServerIDHeaderValue:    a.serverIDHeaderValue,
+		ServerIDHeaderName:     awsauth.IAMServerIDHeaderName,
+		GetEntityMethodHeader:  awsauth.GetEntityMethodHeader,
+		GetEntityURLHeader:     awsauth.GetEntityURLHeader,
+		GetEntityHeadersHeader: awsauth.GetEntityHeadersHeader,
+		GetEntityBodyHeader:    awsauth.GetEntityBodyHeader,
+	})
+	if err != nil {
+		return "", err
+	}
+
+	loginDataJson, err := json.Marshal(loginData)
+	if err != nil {
+		return "", err
+	}
+	return string(loginDataJson), err
+}

command/login/login.go

@@ -36,6 +36,8 @@ type cmd struct {
 	tokenSinkFile   string
 	meta            map[string]string
 
+	aws AWSLogin
+
 	enterpriseCmd
 }
 
@@ -57,10 +59,10 @@ func (c *cmd) init() {
 	c.flags.Var((*flags.FlagMapValue)(&c.meta), "meta",
 		"Metadata to set on the token, formatted as key=value. This flag "+
 			"may be specified multiple times to set multiple meta fields.")
-
 	c.initEnterpriseFlags()
 
 	c.http = &flags.HTTPFlags{}
+	flags.Merge(c.flags, c.aws.flags())
 	flags.Merge(c.flags, c.http.ClientFlags())
 	flags.Merge(c.flags, c.http.ServerFlags())
 	flags.Merge(c.flags, c.http.MultiTenancyFlags())
@@ -89,11 +91,27 @@ func (c *cmd) Run(args []string) int {
 }
 
 func (c *cmd) bearerTokenLogin() int {
-	if c.bearerTokenFile == "" {
+	if err := c.aws.checkFlags(); err != nil {
-		c.UI.Error(fmt.Sprintf("Missing required '-bearer-token-file' flag"))
+		c.UI.Error(err.Error())
 		return 1
 	}
 
+	if c.aws.autoBearerToken {
+		if c.bearerTokenFile != "" {
+			c.UI.Error("Cannot use '-bearer-token-file' flag with '-aws-auto-bearer-token'")
+			return 1
+		}
+
+		if token, err := c.aws.createAWSBearerToken(); err != nil {
+			c.UI.Error(fmt.Sprintf("Error with aws-iam auth method: %s", err))
+			return 1
+		} else {
+			c.bearerToken = token
+		}
+	} else if c.bearerTokenFile == "" {
+		c.UI.Error("Missing required '-bearer-token-file' flag")
+		return 1
+	} else {
 		data, err := ioutil.ReadFile(c.bearerTokenFile)
 		if err != nil {
 			c.UI.Error(err.Error())
@@ -105,6 +123,7 @@ func (c *cmd) bearerTokenLogin() int {
 			c.UI.Error(fmt.Sprintf("No bearer token found in %s", c.bearerTokenFile))
 			return 1
 		}
+	}
 
 	// Ensure that we don't try to use a token when performing a login
 	// operation.

command/login/login_test.go

@@ -1,6 +1,7 @@
 package login
 
 import (
+	"fmt"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -18,6 +19,7 @@ import (
 	"github.com/hashicorp/consul/api"
 	"github.com/hashicorp/consul/command/acl"
 	"github.com/hashicorp/consul/internal/go-sso/oidcauth/oidcauthtest"
+	"github.com/hashicorp/consul/internal/iamauth/iamauthtest"
 	"github.com/hashicorp/consul/sdk/testutil"
 	"github.com/hashicorp/consul/testrpc"
 )
@@ -39,18 +41,7 @@ func TestLoginCommand(t *testing.T) {
 
 	testDir := testutil.TempDir(t, "acl")
 
-	a := agent.NewTestAgent(t, `
+	a := newTestAgent(t)
-	primary_datacenter = "dc1"
-	acl {
-		enabled = true
-		tokens {
-			initial_management = "root"
-		}
-	}`)
-
-	defer a.Shutdown()
-	testrpc.WaitForLeader(t, a.RPC, "dc1")
-
 	client := a.Client()
 
 	t.Run("method is required", func(t *testing.T) {
@@ -102,6 +93,81 @@ func TestLoginCommand(t *testing.T) {
 		require.Contains(t, ui.ErrorWriter.String(), "Missing required '-bearer-token-file' flag")
 	})
 
+	t.Run("bearer-token-file disallowed with aws-auto-bearer-token", func(t *testing.T) {
+		defer os.Remove(tokenSinkFile)
+
+		ui := cli.NewMockUi()
+		cmd := New(ui)
+
+		args := []string{
+			"-http-addr=" + a.HTTPAddr(),
+			"-token=root",
+			"-method=test",
+			"-token-sink-file", tokenSinkFile,
+			"-bearer-token-file", "none.txt",
+			"-aws-auto-bearer-token",
+		}
+
+		code := cmd.Run(args)
+		require.Equal(t, code, 1, "err: %s", ui.ErrorWriter.String())
+		require.Contains(t, ui.ErrorWriter.String(), "Cannot use '-bearer-token-file' flag with '-aws-auto-bearer-token'")
+	})
+
+	t.Run("aws flags require aws-auto-bearer-token", func(t *testing.T) {
+		defer os.Remove(tokenSinkFile)
+
+		baseArgs := []string{
+			"-http-addr=" + a.HTTPAddr(),
+			"-token=root",
+			"-method=test",
+			"-token-sink-file", tokenSinkFile,
+		}
+
+		for _, extraArgs := range [][]string{
+			{"-aws-include-entity"},
+			{"-aws-sts-endpoint", "some-endpoint"},
+			{"-aws-region", "some-region"},
+			{"-aws-server-id-header-value", "some-value"},
+			{"-aws-access-key-id", "some-key"},
+			{"-aws-secret-access-key", "some-secret"},
+			{"-aws-session-token", "some-token"},
+		} {
+			ui := cli.NewMockUi()
+			code := New(ui).Run(append(baseArgs, extraArgs...))
+			require.Equal(t, code, 1, "err: %s", ui.ErrorWriter.String())
+			require.Contains(t, ui.ErrorWriter.String(), "Missing '-aws-auto-bearer-token' flag")
+		}
+	})
+
+	t.Run("aws-access-key-id and aws-secret-access-key require each other", func(t *testing.T) {
+		defer os.Remove(tokenSinkFile)
+
+		baseArgs := []string{
+			"-http-addr=" + a.HTTPAddr(),
+			"-token=root",
+			"-method=test",
+			"-token-sink-file", tokenSinkFile,
+			"-aws-auto-bearer-token",
+		}
+
+		ui := cli.NewMockUi()
+		code := New(ui).Run(append(baseArgs, "-aws-access-key-id", "some-key"))
+		require.Equal(t, code, 1, "err: %s", ui.ErrorWriter.String())
+		require.Contains(t, ui.ErrorWriter.String(), "Missing '-aws-secret-access-key' flag")
+
+		ui = cli.NewMockUi()
+		code = New(ui).Run(append(baseArgs, "-aws-secret-access-key", "some-key"))
+		require.Equal(t, code, 1, "err: %s", ui.ErrorWriter.String())
+		require.Contains(t, ui.ErrorWriter.String(), "Missing '-aws-access-key-id' flag")
+
+		ui = cli.NewMockUi()
+		code = New(ui).Run(append(baseArgs, "-aws-session-token", "some-token"))
+		require.Equal(t, code, 1, "err: %s", ui.ErrorWriter.String())
+		require.Contains(t, ui.ErrorWriter.String(),
+			"Missing '-aws-access-key-id' and '-aws-secret-access-key' flags")
+
+	})
+
 	bearerTokenFile := filepath.Join(testDir, "bearer.token")
 
 	t.Run("bearer-token-file is empty", func(t *testing.T) {
@@ -236,18 +302,7 @@ func TestLoginCommand_k8s(t *testing.T) {
 
 	testDir := testutil.TempDir(t, "acl")
 
-	a := agent.NewTestAgent(t, `
+	a := newTestAgent(t)
-	primary_datacenter = "dc1"
-	acl {
-		enabled = true
-		tokens {
-			initial_management = "root"
-		}
-	}`)
-
-	defer a.Shutdown()
-	testrpc.WaitForLeader(t, a.RPC, "dc1")
-
 	client := a.Client()
 
 	tokenSinkFile := filepath.Join(testDir, "test.token")
@@ -334,18 +389,7 @@ func TestLoginCommand_jwt(t *testing.T) {
 
 	testDir := testutil.TempDir(t, "acl")
 
-	a := agent.NewTestAgent(t, `
+	a := newTestAgent(t)
-	primary_datacenter = "dc1"
-	acl {
-		enabled = true
-		tokens {
-			initial_management = "root"
-		}
-	}`)
-
-	defer a.Shutdown()
-	testrpc.WaitForLeader(t, a.RPC, "dc1")
-
 	client := a.Client()
 
 	tokenSinkFile := filepath.Join(testDir, "test.token")
@@ -470,3 +514,178 @@ func TestLoginCommand_jwt(t *testing.T) {
 		})
 	}
 }
+
+func TestLoginCommand_aws_iam(t *testing.T) {
+	if testing.Short() {
+		t.Skip("too slow for testing.Short")
+	}
+
+	t.Parallel()
+
+	// Formats an HIL template for a BindName, and the expected value for entity tags.
+	// Input:   string{"a", "b"}, []string{"1", "2"}
+	// Return: "${entity_tags.a}-${entity_tags.b}",  "1-2"
+	entityTagsBind := func(keys, values []string) (string, string) {
+		parts := []string{}
+		for _, k := range keys {
+			parts = append(parts, fmt.Sprintf("${entity_tags.%s}", k))
+		}
+		return strings.Join(parts, "-"), strings.Join(values, "-")
+	}
+
+	f := iamauthtest.MakeFixture()
+	roleTagsBindName, roleTagsBindValue := entityTagsBind(f.RoleTagKeys(), f.RoleTagValues())
+	userTagsBindName, userTagsBindValue := entityTagsBind(f.UserTagKeys(), f.UserTagValues())
+
+	cases := map[string]struct {
+		awsServer          *iamauthtest.Server
+		cmdArgs            []string
+		config             map[string]interface{}
+		bindingRule        *api.ACLBindingRule
+		expServiceIdentity *api.ACLServiceIdentity
+	}{
+		"success - login with role": {
+			awsServer: f.ServerForRole,
+			cmdArgs:   []string{"-aws-auto-bearer-token"},
+			config: map[string]interface{}{
+				// Test that an assumed-role arn is translated to the canonical role arn.
+				"BoundIAMPrincipalARNs": []string{f.CanonicalRoleARN},
+			},
+			bindingRule: &api.ACLBindingRule{
+				BindType: api.BindingRuleBindTypeService,
+				BindName: "${entity_name}-${entity_id}-${account_id}",
+				Selector: fmt.Sprintf(`entity_name==%q and entity_id==%q and account_id==%q`,
+					f.RoleName, f.EntityID, f.AccountID),
+			},
+			expServiceIdentity: &api.ACLServiceIdentity{
+				ServiceName: fmt.Sprintf("%s-%s-%s", f.RoleName, strings.ToLower(f.EntityID), f.AccountID),
+			},
+		},
+		"success - login with role and entity details enabled": {
+			awsServer: f.ServerForRole,
+			cmdArgs:   []string{"-aws-auto-bearer-token", "-aws-include-entity"},
+			config: map[string]interface{}{
+				// Test that we can login with full user path.
+				"BoundIAMPrincipalARNs":  []string{f.RoleARN},
+				"EnableIAMEntityDetails": true,
+			},
+			bindingRule: &api.ACLBindingRule{
+				BindType: api.BindingRuleBindTypeService,
+				// TODO: Path cannot be used as service name if it contains a '/'
+				BindName: "${entity_name}",
+				Selector: fmt.Sprintf(`entity_name==%q and entity_path==%q`, f.RoleName, f.RolePath),
+			},
+			expServiceIdentity: &api.ACLServiceIdentity{ServiceName: f.RoleName},
+		},
+		"success - login with role and role tags": {
+			awsServer: f.ServerForRole,
+			cmdArgs:   []string{"-aws-auto-bearer-token", "-aws-include-entity"},
+			config: map[string]interface{}{
+				// Test that we can login with a wildcard.
+				"BoundIAMPrincipalARNs":  []string{f.RoleARNWildcard},
+				"EnableIAMEntityDetails": true,
+				"IAMEntityTags":          f.RoleTagKeys(),
+			},
+			bindingRule: &api.ACLBindingRule{
+				BindType: api.BindingRuleBindTypeService,
+				BindName: roleTagsBindName,
+				Selector: fmt.Sprintf(`entity_name==%q and entity_path==%q`, f.RoleName, f.RolePath),
+			},
+			expServiceIdentity: &api.ACLServiceIdentity{ServiceName: roleTagsBindValue},
+		},
+		"success - login with user and user tags": {
+			awsServer: f.ServerForUser,
+			cmdArgs:   []string{"-aws-auto-bearer-token", "-aws-include-entity"},
+			config: map[string]interface{}{
+				// Test that we can login with a wildcard.
+				"BoundIAMPrincipalARNs":  []string{f.UserARNWildcard},
+				"EnableIAMEntityDetails": true,
+				"IAMEntityTags":          f.UserTagKeys(),
+			},
+			bindingRule: &api.ACLBindingRule{
+				BindType: api.BindingRuleBindTypeService,
+				BindName: "${entity_name}-" + userTagsBindName,
+				Selector: fmt.Sprintf(`entity_name==%q and entity_path==%q`, f.UserName, f.UserPath),
+			},
+			expServiceIdentity: &api.ACLServiceIdentity{
+				ServiceName: fmt.Sprintf("%s-%s", f.UserName, userTagsBindValue),
+			},
+		},
+	}
+
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			a := newTestAgent(t)
+			client := a.Client()
+
+			fakeAws := iamauthtest.NewTestServer(t, c.awsServer)
+
+			c.config["STSEndpoint"] = fakeAws.URL + "/sts"
+			c.config["IAMEndpoint"] = fakeAws.URL + "/iam"
+
+			_, _, err := client.ACL().AuthMethodCreate(
+				&api.ACLAuthMethod{
+					Name:   "iam-test",
+					Type:   "aws-iam",
+					Config: c.config,
+				},
+				&api.WriteOptions{Token: "root"},
+			)
+			require.NoError(t, err)
+
+			c.bindingRule.AuthMethod = "iam-test"
+			_, _, err = client.ACL().BindingRuleCreate(
+				c.bindingRule,
+				&api.WriteOptions{Token: "root"},
+			)
+			require.NoError(t, err)
+
+			testDir := testutil.TempDir(t, "acl")
+			tokenSinkFile := filepath.Join(testDir, "test.token")
+			t.Cleanup(func() { _ = os.Remove(tokenSinkFile) })
+
+			ui := cli.NewMockUi()
+			cmd := New(ui)
+			args := []string{
+				"-http-addr=" + a.HTTPAddr(),
+				"-token=root",
+				"-method=iam-test",
+				"-token-sink-file", tokenSinkFile,
+				"-aws-sts-endpoint", fakeAws.URL + "/sts",
+				"-aws-region", "fake-region",
+				"-aws-access-key-id", "fake-key-id",
+				"-aws-secret-access-key", "fake-secret-key",
+			}
+			args = append(args, c.cmdArgs...)
+			code := cmd.Run(args)
+			require.Equal(t, 0, code, ui.ErrorWriter.String())
+
+			raw, err := ioutil.ReadFile(tokenSinkFile)
+			require.NoError(t, err)
+
+			token := strings.TrimSpace(string(raw))
+			require.Len(t, token, 36, "must be a valid uid: %s", token)
+
+			// Validate correct BindName was interpolated.
+			tokenRead, _, err := client.ACL().TokenReadSelf(&api.QueryOptions{Token: token})
+			require.NoError(t, err)
+			require.Len(t, tokenRead.ServiceIdentities, 1)
+			require.Equal(t, c.expServiceIdentity, tokenRead.ServiceIdentities[0])
+
+		})
+	}
+}
+
+func newTestAgent(t *testing.T) *agent.TestAgent {
+	a := agent.NewTestAgent(t, `
+	primary_datacenter = "dc1"
+	acl {
+		enabled = true
+		tokens {
+			initial_management = "root"
+		}
+	}`)
+	t.Cleanup(func() { _ = a.Shutdown() })
+	testrpc.WaitForLeader(t, a.RPC, "dc1")
+	return a
+}

go.mod

@@ -44,7 +44,7 @@ require (
 	github.com/hashicorp/go-memdb v1.3.2
 	github.com/hashicorp/go-multierror v1.1.1
 	github.com/hashicorp/go-raftchunking v0.6.2
-	github.com/hashicorp/go-retryablehttp v0.6.7 // indirect
+	github.com/hashicorp/go-retryablehttp v0.6.7
 	github.com/hashicorp/go-sockaddr v1.0.2
 	github.com/hashicorp/go-syslog v1.0.0
 	github.com/hashicorp/go-uuid v1.0.2

internal/iamauth/README.md

@@ -0,0 +1,2 @@
+This is an internal package to house the AWS IAM auth method utilities for potential
+future extraction from Consul.

internal/iamauth/auth.go

@@ -0,0 +1,311 @@
+package iamauth
+
+import (
+	"context"
+	"encoding/xml"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"regexp"
+	"strings"
+	"time"
+
+	"github.com/hashicorp/consul/internal/iamauth/responses"
+	"github.com/hashicorp/consul/lib"
+	"github.com/hashicorp/consul/lib/stringslice"
+	"github.com/hashicorp/go-cleanhttp"
+	"github.com/hashicorp/go-hclog"
+	"github.com/hashicorp/go-retryablehttp"
+)
+
+const (
+	// Retry configuration
+	retryWaitMin = 500 * time.Millisecond
+	retryWaitMax = 30 * time.Second
+)
+
+type Authenticator struct {
+	config *Config
+	logger hclog.Logger
+}
+
+type IdentityDetails struct {
+	EntityName string
+	EntityId   string
+	AccountId  string
+
+	EntityPath string
+	EntityTags map[string]string
+}
+
+func NewAuthenticator(config *Config, logger hclog.Logger) (*Authenticator, error) {
+	if err := config.Validate(); err != nil {
+		return nil, err
+	}
+	return &Authenticator{
+		config: config,
+		logger: logger,
+	}, nil
+}
+
+// ValidateLogin determines if the identity in the loginToken is permitted to login.
+// If so, it returns details about the identity. Otherwise, an error is returned.
+func (a *Authenticator) ValidateLogin(ctx context.Context, loginToken string) (*IdentityDetails, error) {
+	token, err := NewBearerToken(loginToken, a.config)
+	if err != nil {
+		return nil, err
+	}
+
+	req, err := token.GetCallerIdentityRequest()
+	if err != nil {
+		return nil, err
+	}
+
+	if a.config.ServerIDHeaderValue != "" {
+		err := validateHeaderValue(req.Header, a.config.ServerIDHeaderName, a.config.ServerIDHeaderValue)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	callerIdentity, err := a.submitCallerIdentityRequest(ctx, req)
+	if err != nil {
+		return nil, err
+	}
+	a.logger.Debug("iamauth login attempt", "arn", callerIdentity.Arn)
+
+	entity, err := responses.ParseArn(callerIdentity.Arn)
+	if err != nil {
+		return nil, err
+	}
+
+	identityDetails := &IdentityDetails{
+		EntityName: entity.FriendlyName,
+		// This could either be a "userID:SessionID" (in the case of an assumed role) or just a "userID"
+		// (in the case of an IAM user).
+		EntityId:  strings.Split(callerIdentity.UserId, ":")[0],
+		AccountId: callerIdentity.Account,
+	}
+	clientArn := entity.CanonicalArn()
+
+	// Fetch the IAM Role or IAM User, if configured.
+	// This requires the token to contain a signed iam:GetRole or iam:GetUser request.
+	if a.config.EnableIAMEntityDetails {
+		iamReq, err := token.GetEntityRequest()
+		if err != nil {
+			return nil, err
+		}
+
+		if a.config.ServerIDHeaderValue != "" {
+			err := validateHeaderValue(iamReq.Header, a.config.ServerIDHeaderName, a.config.ServerIDHeaderValue)
+			if err != nil {
+				return nil, err
+			}
+		}
+
+		iamEntityDetails, err := a.submitGetIAMEntityRequest(ctx, iamReq, token.entityRequestType)
+		if err != nil {
+			return nil, err
+		}
+
+		// Only the CallerIdentity response is a guarantee of the client's identity.
+		// The role/user details must have a unique id match to the CallerIdentity before use.
+		if iamEntityDetails.EntityId() != identityDetails.EntityId {
+			return nil, fmt.Errorf("unique id mismatch in login token")
+		}
+
+		// Use the full ARN with path from the Role/User details
+		clientArn = iamEntityDetails.EntityArn()
+		identityDetails.EntityPath = iamEntityDetails.EntityPath()
+		identityDetails.EntityTags = iamEntityDetails.EntityTags()
+	}
+
+	if err := a.validateIdentity(clientArn); err != nil {
+		return nil, err
+	}
+	return identityDetails, nil
+}
+
+// https://github.com/hashicorp/vault/blob/ba533d006f2244103648785ebfe8a9a9763d2b6e/builtin/credential/aws/path_login.go#L1321-L1361
+func (a *Authenticator) validateIdentity(clientArn string) error {
+	if stringslice.Contains(a.config.BoundIAMPrincipalARNs, clientArn) {
+		// Matches one of BoundIAMPrincipalARNs, so it is trusted
+		return nil
+	}
+	if a.config.EnableIAMEntityDetails {
+		for _, principalArn := range a.config.BoundIAMPrincipalARNs {
+			if strings.HasSuffix(principalArn, "*") && lib.GlobbedStringsMatch(principalArn, clientArn) {
+				// Wildcard match, so it is trusted
+				return nil
+			}
+		}
+	}
+	return fmt.Errorf("IAM principal %s is not trusted", clientArn)
+}
+
+func (a *Authenticator) submitCallerIdentityRequest(ctx context.Context, req *http.Request) (*responses.GetCallerIdentityResult, error) {
+	responseBody, err := a.submitRequest(ctx, req)
+	if err != nil {
+		return nil, err
+	}
+	callerIdentityResponse, err := parseGetCallerIdentityResponse(responseBody)
+	if err != nil {
+		return nil, fmt.Errorf("error parsing STS response")
+	}
+
+	if n := len(callerIdentityResponse.GetCallerIdentityResult); n != 1 {
+		return nil, fmt.Errorf("received %d identities in STS response but expected 1", n)
+	}
+	return &callerIdentityResponse.GetCallerIdentityResult[0], nil
+}
+
+func (a *Authenticator) submitGetIAMEntityRequest(ctx context.Context, req *http.Request, reqType string) (responses.IAMEntity, error) {
+	responseBody, err := a.submitRequest(ctx, req)
+	if err != nil {
+		return nil, err
+	}
+	iamResponse, err := parseGetIAMEntityResponse(responseBody, reqType)
+	if err != nil {
+		return nil, fmt.Errorf("error parsing IAM response: %s", err)
+	}
+	return iamResponse, nil
+
+}
+
+// https://github.com/hashicorp/vault/blob/b17e3256dde937a6248c9a2fa56206aac93d07de/builtin/credential/aws/path_login.go#L1636
+func (a *Authenticator) submitRequest(ctx context.Context, req *http.Request) (string, error) {
+	retryableReq, err := retryablehttp.FromRequest(req)
+	if err != nil {
+		return "", err
+	}
+	retryableReq = retryableReq.WithContext(ctx)
+	client := cleanhttp.DefaultClient()
+	client.CheckRedirect = func(req *http.Request, via []*http.Request) error {
+		return http.ErrUseLastResponse
+	}
+	retryingClient := &retryablehttp.Client{
+		HTTPClient:   client,
+		RetryWaitMin: retryWaitMin,
+		RetryWaitMax: retryWaitMax,
+		RetryMax:     a.config.MaxRetries,
+		CheckRetry:   retryablehttp.DefaultRetryPolicy,
+		Backoff:      retryablehttp.DefaultBackoff,
+	}
+
+	response, err := retryingClient.Do(retryableReq)
+	if err != nil {
+		return "", fmt.Errorf("error making request: %w", err)
+	}
+	if response != nil {
+		defer response.Body.Close()
+	}
+	// Validate that the response type is XML
+	if ct := response.Header.Get("Content-Type"); ct != "text/xml" {
+		return "", fmt.Errorf("response body is invalid")
+	}
+
+	// we check for status code afterwards to also print out response body
+	responseBody, err := ioutil.ReadAll(response.Body)
+	if err != nil {
+		return "", err
+	}
+	if response.StatusCode != 200 {
+		return "", fmt.Errorf("received error code %d: %s", response.StatusCode, string(responseBody))
+	}
+	return string(responseBody), nil
+
+}
+
+// https://github.com/hashicorp/vault/blob/ba533d006f2244103648785ebfe8a9a9763d2b6e/builtin/credential/aws/path_login.go#L1625-L1634
+func parseGetCallerIdentityResponse(response string) (responses.GetCallerIdentityResponse, error) {
+	result := responses.GetCallerIdentityResponse{}
+	response = strings.TrimSpace(response)
+	if !strings.HasPrefix(response, "<GetCallerIdentityResponse") && !strings.HasPrefix(response, "<?xml") {
+		return result, fmt.Errorf("body of GetCallerIdentity is invalid")
+	}
+	decoder := xml.NewDecoder(strings.NewReader(response))
+	err := decoder.Decode(&result)
+	return result, err
+}
+
+func parseGetIAMEntityResponse(response string, reqType string) (responses.IAMEntity, error) {
+	if !strings.HasPrefix(response, "<GetRoleResponse") &&
+		!strings.HasPrefix(response, "<GetUserResponse") &&
+		!strings.HasPrefix(response, "<?xml") {
+		return nil, fmt.Errorf("body of GetRole or GetUser is invalid")
+	}
+
+	decoder := xml.NewDecoder(strings.NewReader(response))
+
+	switch reqType {
+	case "GetRole":
+		result := &responses.GetRoleResponse{}
+		err := decoder.Decode(&result)
+		if err != nil {
+			return nil, err
+		}
+		if n := len(result.GetRoleResult); n != 1 {
+			return nil, fmt.Errorf("received %d identities in GetRole response but expected 1", n)
+		}
+		return &result.GetRoleResult[0].Role, nil
+	case "GetUser":
+		result := &responses.GetUserResponse{}
+		err := decoder.Decode(&result)
+		if err != nil {
+			return nil, err
+		}
+		if n := len(result.GetUserResult); n != 1 {
+			return nil, fmt.Errorf("received %d identities in GetUser response but expected 1", n)
+		}
+		return &result.GetUserResult[0].User, nil
+	}
+	return nil, fmt.Errorf("invalid %s request: %s", reqType, response)
+}
+
+// https://github.com/hashicorp/vault/blob/b17e3256dde937a6248c9a2fa56206aac93d07de/builtin/credential/aws/path_login.go#L1532
+func validateHeaderValue(headers http.Header, headerName string, requiredHeaderValue string) error {
+	providedValue := ""
+	for k, v := range headers {
+		if strings.EqualFold(headerName, k) {
+			providedValue = strings.Join(v, ",")
+			break
+		}
+	}
+	if providedValue == "" {
+		return fmt.Errorf("missing header %q", headerName)
+	}
+
+	// NOT doing a constant time compare here since the value is NOT intended to be secret
+	if providedValue != requiredHeaderValue {
+		return fmt.Errorf("expected %q but got %q", requiredHeaderValue, providedValue)
+	}
+
+	if authzHeaders, ok := headers["Authorization"]; ok {
+		// authzHeader looks like AWS4-HMAC-SHA256 Credential=AKI..., SignedHeaders=host;x-amz-date;x-vault-awsiam-id, Signature=...
+		// We need to extract out the SignedHeaders
+		re := regexp.MustCompile(".*SignedHeaders=([^,]+)")
+		authzHeader := strings.Join(authzHeaders, ",")
+		matches := re.FindSubmatch([]byte(authzHeader))
+		if len(matches) < 1 {
+			return fmt.Errorf("server id header wasn't signed")
+		}
+		if len(matches) > 2 {
+			return fmt.Errorf("found multiple SignedHeaders components")
+		}
+		signedHeaders := string(matches[1])
+		return ensureHeaderIsSigned(signedHeaders, headerName)
+	}
+	// NOTE: If we support GET requests, then we need to parse the X-Amz-SignedHeaders
+	// argument out of the query string and search in there for the header value
+	return fmt.Errorf("missing Authorization header")
+}
+
+func ensureHeaderIsSigned(signedHeaders, headerToSign string) error {
+	// Not doing a constant time compare here, the values aren't secret
+	for _, header := range strings.Split(signedHeaders, ";") {
+		if header == strings.ToLower(headerToSign) {
+			return nil
+		}
+	}
+	return fmt.Errorf("header wasn't signed")
+}

internal/iamauth/auth_test.go

@@ -0,0 +1,123 @@
+package iamauth
+
+import (
+	"context"
+	"encoding/json"
+	"testing"
+
+	"github.com/aws/aws-sdk-go/aws/credentials"
+	"github.com/hashicorp/consul/internal/iamauth/iamauthtest"
+	"github.com/hashicorp/consul/internal/iamauth/responsestest"
+	"github.com/hashicorp/go-hclog"
+	"github.com/stretchr/testify/require"
+)
+
+func TestValidateLogin(t *testing.T) {
+	f := iamauthtest.MakeFixture()
+
+	var (
+		serverForRoleMismatchedIds = &iamauthtest.Server{
+			GetCallerIdentityResponse: f.ServerForRole.GetCallerIdentityResponse,
+			GetRoleResponse:           responsestest.MakeGetRoleResponse(f.RoleARN, "AAAAsomenonmatchingid"),
+		}
+		serverForUserMismatchedIds = &iamauthtest.Server{
+			GetCallerIdentityResponse: f.ServerForUser.GetCallerIdentityResponse,
+			GetUserResponse:           responsestest.MakeGetUserResponse(f.UserARN, "AAAAsomenonmatchingid"),
+		}
+	)
+
+	cases := map[string]struct {
+		config   *Config
+		server   *iamauthtest.Server
+		expIdent *IdentityDetails
+		expError string
+	}{
+		"no bound principals": {
+			expError: "not trusted",
+			server:   f.ServerForRole,
+			config:   &Config{},
+		},
+		"no matching principal": {
+			expError: "not trusted",
+			server:   f.ServerForUser,
+			config: &Config{
+				BoundIAMPrincipalARNs: []string{
+					"arn:aws:iam::1234567890:user/some-other-role",
+					"arn:aws:iam::1234567890:user/some-other-user",
+				},
+			},
+		},
+		"mismatched server id header": {
+			expError: `expected "some-non-matching-value" but got "server.id.example.com"`,
+			server:   f.ServerForRole,
+			config: &Config{
+				BoundIAMPrincipalARNs: []string{f.CanonicalRoleARN},
+				ServerIDHeaderValue:   "some-non-matching-value",
+				ServerIDHeaderName:    "X-Test-ServerID",
+			},
+		},
+		"role unique id mismatch": {
+			expError: "unique id mismatch in login token",
+			// The RoleId in the GetRole response must match the UserId in the GetCallerIdentity response
+			// during login. If not, the RoleId cannot be used.
+			server: serverForRoleMismatchedIds,
+			config: &Config{
+				BoundIAMPrincipalARNs:  []string{f.RoleARN},
+				EnableIAMEntityDetails: true,
+			},
+		},
+		"user unique id mismatch": {
+			expError: "unique id mismatch in login token",
+			server:   serverForUserMismatchedIds,
+			config: &Config{
+				BoundIAMPrincipalARNs:  []string{f.UserARN},
+				EnableIAMEntityDetails: true,
+			},
+		},
+	}
+	logger := hclog.New(nil)
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			fakeAws := iamauthtest.NewTestServer(t, c.server)
+
+			c.config.STSEndpoint = fakeAws.URL + "/sts"
+			c.config.IAMEndpoint = fakeAws.URL + "/iam"
+			setTestHeaderNames(c.config)
+
+			// This bypasses NewAuthenticator, which bypasses config.Validate().
+			auth := &Authenticator{config: c.config, logger: logger}
+
+			loginInput := &LoginInput{
+				Creds:               credentials.NewStaticCredentials("fake", "fake", ""),
+				IncludeIAMEntity:    c.config.EnableIAMEntityDetails,
+				STSEndpoint:         c.config.STSEndpoint,
+				STSRegion:           "fake-region",
+				Logger:              logger,
+				ServerIDHeaderValue: "server.id.example.com",
+			}
+			setLoginInputHeaderNames(loginInput)
+			loginData, err := GenerateLoginData(loginInput)
+			require.NoError(t, err)
+			loginBytes, err := json.Marshal(loginData)
+			require.NoError(t, err)
+
+			ident, err := auth.ValidateLogin(context.Background(), string(loginBytes))
+			if c.expError != "" {
+				require.Error(t, err)
+				require.Contains(t, err.Error(), c.expError)
+				require.Nil(t, ident)
+			} else {
+				require.NoError(t, err)
+				require.Equal(t, c.expIdent, ident)
+			}
+		})
+	}
+}
+
+func setLoginInputHeaderNames(in *LoginInput) {
+	in.ServerIDHeaderName = "X-Test-ServerID"
+	in.GetEntityMethodHeader = "X-Test-Method"
+	in.GetEntityURLHeader = "X-Test-URL"
+	in.GetEntityHeadersHeader = "X-Test-Headers"
+	in.GetEntityBodyHeader = "X-Test-Body"
+}

internal/iamauth/config.go

@@ -0,0 +1,69 @@
+package iamauth
+
+import (
+	"fmt"
+	"strings"
+
+	awsArn "github.com/aws/aws-sdk-go/aws/arn"
+)
+
+type Config struct {
+	BoundIAMPrincipalARNs  []string
+	EnableIAMEntityDetails bool
+	IAMEntityTags          []string
+	ServerIDHeaderValue    string
+	MaxRetries             int
+	IAMEndpoint            string
+	STSEndpoint            string
+	STSRegion              string
+	AllowedSTSHeaderValues []string
+
+	// Customizable header names
+	ServerIDHeaderName     string
+	GetEntityMethodHeader  string
+	GetEntityURLHeader     string
+	GetEntityHeadersHeader string
+	GetEntityBodyHeader    string
+}
+
+func (c *Config) Validate() error {
+	if len(c.BoundIAMPrincipalARNs) == 0 {
+		return fmt.Errorf("BoundIAMPrincipalARNs is required and must have at least 1 entry")
+	}
+
+	for _, arn := range c.BoundIAMPrincipalARNs {
+		if n := strings.Count(arn, "*"); n > 0 {
+			if !c.EnableIAMEntityDetails {
+				return fmt.Errorf("Must set EnableIAMEntityDetails=true to use wildcards in BoundIAMPrincipalARNs")
+			}
+			if n != 1 || !strings.HasSuffix(arn, "*") {
+				return fmt.Errorf("Only one wildcard is allowed at the end of the bound IAM principal ARN")
+			}
+		}
+
+		if parsed, err := awsArn.Parse(arn); err != nil {
+			return fmt.Errorf("Invalid principal ARN: %q", arn)
+		} else if parsed.Service != "iam" && parsed.Service != "sts" {
+			return fmt.Errorf("Invalid principal ARN: %q", arn)
+		}
+	}
+
+	if len(c.IAMEntityTags) > 0 && !c.EnableIAMEntityDetails {
+		return fmt.Errorf("Must set EnableIAMEntityDetails=true to use IAMUserTags")
+	}
+
+	// If server id header checking is enabled, we need the header name.
+	if c.ServerIDHeaderValue != "" && c.ServerIDHeaderName == "" {
+		return fmt.Errorf("Must set ServerIDHeaderName to use a server ID value")
+	}
+
+	if c.EnableIAMEntityDetails && (c.GetEntityBodyHeader == "" ||
+		c.GetEntityHeadersHeader == "" ||
+		c.GetEntityMethodHeader == "" ||
+		c.GetEntityURLHeader == "") {
+		return fmt.Errorf("Must set all of GetEntityMethodHeader, GetEntityURLHeader, " +
+			"GetEntityHeadersHeader, and GetEntityBodyHeader when EnableIAMEntityDetails=true")
+	}
+
+	return nil
+}

internal/iamauth/config_test.go

@@ -0,0 +1,150 @@
+package iamauth
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestConfigValidate(t *testing.T) {
+	principalArn := "arn:aws:iam::000000000000:role/my-role"
+
+	cases := map[string]struct {
+		expError string
+		configs  []Config
+
+		includeHeaderNames bool
+	}{
+		"bound iam principals are required": {
+			expError: "BoundIAMPrincipalARNs is required and must have at least 1 entry",
+			configs: []Config{
+				{BoundIAMPrincipalARNs: nil},
+				{BoundIAMPrincipalARNs: []string{}},
+			},
+		},
+		"entity tags require entity details": {
+			expError: "Must set EnableIAMEntityDetails=true to use IAMUserTags",
+			configs: []Config{
+				{
+					BoundIAMPrincipalARNs:  []string{principalArn},
+					EnableIAMEntityDetails: false,
+					IAMEntityTags:          []string{"some-tag"},
+				},
+			},
+		},
+		"entity details require all entity header names": {
+			expError: "Must set all of GetEntityMethodHeader, GetEntityURLHeader, " +
+				"GetEntityHeadersHeader, and GetEntityBodyHeader when EnableIAMEntityDetails=true",
+			configs: []Config{
+				{
+					BoundIAMPrincipalARNs:  []string{principalArn},
+					EnableIAMEntityDetails: true,
+				},
+				{
+					BoundIAMPrincipalARNs:  []string{principalArn},
+					EnableIAMEntityDetails: true,
+					GetEntityBodyHeader:    "X-Test-Header",
+				},
+				{
+					BoundIAMPrincipalARNs:  []string{principalArn},
+					EnableIAMEntityDetails: true,
+					GetEntityHeadersHeader: "X-Test-Header",
+				},
+				{
+					BoundIAMPrincipalARNs:  []string{principalArn},
+					EnableIAMEntityDetails: true,
+					GetEntityURLHeader:     "X-Test-Header",
+				},
+				{
+					BoundIAMPrincipalARNs:  []string{principalArn},
+					EnableIAMEntityDetails: true,
+					GetEntityMethodHeader:  "X-Test-Header",
+				},
+			},
+		},
+		"wildcard principals require entity details": {
+			expError: "Must set EnableIAMEntityDetails=true to use wildcards in BoundIAMPrincipalARNs",
+			configs: []Config{
+				{BoundIAMPrincipalARNs: []string{"arn:aws:iam::000000000000:role/*"}},
+				{BoundIAMPrincipalARNs: []string{"arn:aws:iam::000000000000:role/path/*"}},
+			},
+		},
+		"only one wildcard suffix is allowed": {
+			expError: "Only one wildcard is allowed at the end of the bound IAM principal ARN",
+			configs: []Config{
+				{
+					BoundIAMPrincipalARNs:  []string{"arn:aws:iam::000000000000:role/**"},
+					EnableIAMEntityDetails: true,
+				},
+				{
+					BoundIAMPrincipalARNs:  []string{"arn:aws:iam::000000000000:role/*/*"},
+					EnableIAMEntityDetails: true,
+				},
+				{
+					BoundIAMPrincipalARNs:  []string{"arn:aws:iam::000000000000:role/*/path"},
+					EnableIAMEntityDetails: true,
+				},
+				{
+					BoundIAMPrincipalARNs:  []string{"arn:aws:iam::000000000000:role/*/path/*"},
+					EnableIAMEntityDetails: true,
+				},
+			},
+		},
+		"invalid principal arns are disallowed": {
+			expError: fmt.Sprintf("Invalid principal ARN"),
+			configs: []Config{
+				{BoundIAMPrincipalARNs: []string{""}},
+				{BoundIAMPrincipalARNs: []string{"  "}},
+				{BoundIAMPrincipalARNs: []string{"*"}, EnableIAMEntityDetails: true},
+				{BoundIAMPrincipalARNs: []string{"arn:aws:iam:role/my-role"}},
+			},
+		},
+		"valid principal arns are allowed": {
+			includeHeaderNames: true,
+			configs: []Config{
+				{BoundIAMPrincipalARNs: []string{"arn:aws:sts::000000000000:assumed-role/my-role/some-session-name"}},
+				{BoundIAMPrincipalARNs: []string{"arn:aws:iam::000000000000:user/my-user"}},
+				{BoundIAMPrincipalARNs: []string{"arn:aws:iam::000000000000:role/my-role"}},
+				{BoundIAMPrincipalARNs: []string{"arn:aws:iam::000000000000:*"}, EnableIAMEntityDetails: true},
+				{BoundIAMPrincipalARNs: []string{"arn:aws:iam::000000000000:role/*"}, EnableIAMEntityDetails: true},
+				{BoundIAMPrincipalARNs: []string{"arn:aws:iam::000000000000:role/path/*"}, EnableIAMEntityDetails: true},
+				{BoundIAMPrincipalARNs: []string{"arn:aws:iam::000000000000:user/*"}, EnableIAMEntityDetails: true},
+				{BoundIAMPrincipalARNs: []string{"arn:aws:iam::000000000000:user/path/*"}, EnableIAMEntityDetails: true},
+			},
+		},
+		"server id header value requires service id header name": {
+			expError: "Must set ServerIDHeaderName to use a server ID value",
+			configs: []Config{
+				{
+					BoundIAMPrincipalARNs: []string{principalArn},
+					ServerIDHeaderValue:   "consul.test.example.com",
+				},
+			},
+		},
+	}
+
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			for _, conf := range c.configs {
+				if c.includeHeaderNames {
+					setTestHeaderNames(&conf)
+				}
+				err := conf.Validate()
+				if c.expError != "" {
+					require.Error(t, err)
+					require.Contains(t, err.Error(), c.expError)
+				} else {
+					require.NoError(t, err)
+				}
+			}
+		})
+	}
+}
+
+func setTestHeaderNames(conf *Config) {
+	conf.GetEntityMethodHeader = "X-Test-Method"
+	conf.GetEntityURLHeader = "X-Test-URL"
+	conf.GetEntityHeadersHeader = "X-Test-Headers"
+	conf.GetEntityBodyHeader = "X-Test-Body"
+}

internal/iamauth/iamauthtest/testing.go

@@ -0,0 +1,187 @@
+package iamauthtest
+
+import (
+	"encoding/xml"
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"sort"
+	"strings"
+	"testing"
+
+	"github.com/hashicorp/consul/internal/iamauth/responses"
+	"github.com/hashicorp/consul/internal/iamauth/responsestest"
+)
+
+// NewTestServer returns a fake AWS API server for local tests:
+// It supports the following paths:
+//   /sts returns STS API responses
+//   /iam returns IAM API responses
+func NewTestServer(t *testing.T, s *Server) *httptest.Server {
+	server := httptest.NewUnstartedServer(s)
+	t.Cleanup(server.Close)
+	server.Start()
+	return server
+}
+
+// Server contains configuration for the fake AWS API server.
+type Server struct {
+	GetCallerIdentityResponse responses.GetCallerIdentityResponse
+	GetRoleResponse           responses.GetRoleResponse
+	GetUserResponse           responses.GetUserResponse
+}
+
+func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if r.Method != "POST" {
+		writeError(w, http.StatusBadRequest, r)
+		return
+	}
+
+	switch {
+	case strings.HasPrefix(r.URL.Path, "/sts"):
+		writeXML(w, s.GetCallerIdentityResponse)
+	case strings.HasPrefix(r.URL.Path, "/iam"):
+		if bodyBytes, err := io.ReadAll(r.Body); err == nil {
+			body := string(bodyBytes)
+			switch {
+			case strings.Contains(body, "Action=GetRole"):
+				writeXML(w, s.GetRoleResponse)
+				return
+			case strings.Contains(body, "Action=GetUser"):
+				writeXML(w, s.GetUserResponse)
+				return
+			}
+		}
+		writeError(w, http.StatusBadRequest, r)
+	default:
+		writeError(w, http.StatusNotFound, r)
+	}
+}
+
+func writeXML(w http.ResponseWriter, val interface{}) {
+	str, err := xml.MarshalIndent(val, "", " ")
+	if err != nil {
+		w.WriteHeader(http.StatusInternalServerError)
+		fmt.Fprint(w, err.Error())
+		return
+	}
+	w.Header().Add("Content-Type", "text/xml")
+	w.WriteHeader(http.StatusOK)
+	fmt.Fprint(w, string(str))
+}
+
+func writeError(w http.ResponseWriter, code int, r *http.Request) {
+	w.WriteHeader(code)
+	msg := fmt.Sprintf("%s %s", r.Method, r.URL)
+	fmt.Fprintf(w, `<ErrorResponse xmlns="https://fakeaws/">
+  <Error>
+	<Message>Fake AWS Server Error: %s</Message>
+  </Error>
+</ErrorResponse>`, msg)
+}
+
+type Fixture struct {
+	AssumedRoleARN   string
+	CanonicalRoleARN string
+	RoleARN          string
+	RoleARNWildcard  string
+	RoleName         string
+	RolePath         string
+	RoleTags         map[string]string
+
+	EntityID            string
+	EntityIDWithSession string
+	AccountID           string
+
+	UserARN         string
+	UserARNWildcard string
+	UserName        string
+	UserPath        string
+	UserTags        map[string]string
+
+	ServerForRole *Server
+	ServerForUser *Server
+}
+
+func MakeFixture() Fixture {
+	f := Fixture{
+		AssumedRoleARN:   "arn:aws:sts::1234567890:assumed-role/my-role/some-session",
+		CanonicalRoleARN: "arn:aws:iam::1234567890:role/my-role",
+		RoleARN:          "arn:aws:iam::1234567890:role/some/path/my-role",
+		RoleARNWildcard:  "arn:aws:iam::1234567890:role/some/path/*",
+		RoleName:         "my-role",
+		RolePath:         "some/path",
+		RoleTags: map[string]string{
+			"service-name": "my-service",
+			"env":          "my-env",
+		},
+
+		EntityID:            "AAAsomeuniqueid",
+		EntityIDWithSession: "AAAsomeuniqueid:some-session",
+		AccountID:           "1234567890",
+
+		UserARN:         "arn:aws:iam::1234567890:user/my-user",
+		UserARNWildcard: "arn:aws:iam::1234567890:user/*",
+		UserName:        "my-user",
+		UserPath:        "",
+		UserTags:        map[string]string{"user-group": "my-group"},
+	}
+
+	f.ServerForRole = &Server{
+		GetCallerIdentityResponse: responsestest.MakeGetCallerIdentityResponse(
+			f.AssumedRoleARN, f.EntityIDWithSession, f.AccountID,
+		),
+		GetRoleResponse: responsestest.MakeGetRoleResponse(
+			f.RoleARN, f.EntityID, toTags(f.RoleTags)...,
+		),
+	}
+
+	f.ServerForUser = &Server{
+		GetCallerIdentityResponse: responsestest.MakeGetCallerIdentityResponse(
+			f.UserARN, f.EntityID, f.AccountID,
+		),
+		GetUserResponse: responsestest.MakeGetUserResponse(
+			f.UserARN, f.EntityID, toTags(f.UserTags)...,
+		),
+	}
+
+	return f
+}
+
+func (f *Fixture) RoleTagKeys() []string   { return keys(f.RoleTags) }
+func (f *Fixture) UserTagKeys() []string   { return keys(f.UserTags) }
+func (f *Fixture) RoleTagValues() []string { return values(f.RoleTags) }
+func (f *Fixture) UserTagValues() []string { return values(f.UserTags) }
+
+// toTags converts the map to a slice of responses.Tag
+func toTags(tags map[string]string) []responses.Tag {
+	result := []responses.Tag{}
+	for k, v := range tags {
+		result = append(result, responses.Tag{
+			Key:   k,
+			Value: v,
+		})
+	}
+	return result
+
+}
+
+// keys returns the keys in sorted order
+func keys(tags map[string]string) []string {
+	result := []string{}
+	for k := range tags {
+		result = append(result, k)
+	}
+	sort.Strings(result)
+	return result
+}
+
+// values returns values in tags, ordered by sorted keys
+func values(tags map[string]string) []string {
+	result := []string{}
+	for _, k := range keys(tags) { // ensures sorted by key
+		result = append(result, tags[k])
+	}
+	return result
+}

internal/iamauth/responses/arn.go

@@ -0,0 +1,94 @@
+package responses
+
+import (
+	"fmt"
+	"strings"
+)
+
+// https://github.com/hashicorp/vault/blob/ba533d006f2244103648785ebfe8a9a9763d2b6e/builtin/credential/aws/path_login.go#L1722-L1744
+type ParsedArn struct {
+	Partition     string
+	AccountNumber string
+	Type          string
+	Path          string
+	FriendlyName  string
+	SessionInfo   string
+}
+
+// https://github.com/hashicorp/vault/blob/ba533d006f2244103648785ebfe8a9a9763d2b6e/builtin/credential/aws/path_login.go#L1482-L1530
+// However, instance profiles are not support in Consul.
+func ParseArn(iamArn string) (*ParsedArn, error) {
+	// iamArn should look like one of the following:
+	// 1. arn:aws:iam::<account_id>:<entity_type>/<UserName>
+	// 2. arn:aws:sts::<account_id>:assumed-role/<RoleName>/<RoleSessionName>
+	// if we get something like 2, then we want to transform that back to what
+	// most people would expect, which is arn:aws:iam::<account_id>:role/<RoleName>
+	var entity ParsedArn
+	fullParts := strings.Split(iamArn, ":")
+	if len(fullParts) != 6 {
+		return nil, fmt.Errorf("unrecognized arn: contains %d colon-separated parts, expected 6", len(fullParts))
+	}
+	if fullParts[0] != "arn" {
+		return nil, fmt.Errorf("unrecognized arn: does not begin with \"arn:\"")
+	}
+	// normally aws, but could be aws-cn or aws-us-gov
+	entity.Partition = fullParts[1]
+	if entity.Partition == "" {
+		return nil, fmt.Errorf("unrecognized arn: %q is missing the partition", iamArn)
+	}
+	if fullParts[2] != "iam" && fullParts[2] != "sts" {
+		return nil, fmt.Errorf("unrecognized service: %v, not one of iam or sts", fullParts[2])
+	}
+	// fullParts[3] is the region, which doesn't matter for AWS IAM entities
+	entity.AccountNumber = fullParts[4]
+	if entity.AccountNumber == "" {
+		return nil, fmt.Errorf("unrecognized arn: %q is missing the account number", iamArn)
+	}
+	// fullParts[5] would now be something like user/<UserName> or assumed-role/<RoleName>/<RoleSessionName>
+	parts := strings.Split(fullParts[5], "/")
+	if len(parts) < 2 {
+		return nil, fmt.Errorf("unrecognized arn: %q contains fewer than 2 slash-separated parts", fullParts[5])
+	}
+	entity.Type = parts[0]
+	entity.Path = strings.Join(parts[1:len(parts)-1], "/")
+	entity.FriendlyName = parts[len(parts)-1]
+	// now, entity.FriendlyName should either be <UserName> or <RoleName>
+	switch entity.Type {
+	case "assumed-role":
+		// Check for three parts for assumed role ARNs
+		if len(parts) < 3 {
+			return nil, fmt.Errorf("unrecognized arn: %q contains fewer than 3 slash-separated parts", fullParts[5])
+		}
+		// Assumed roles don't have paths and have a slightly different format
+		// parts[2] is <RoleSessionName>
+		entity.Path = ""
+		entity.FriendlyName = parts[1]
+		entity.SessionInfo = parts[2]
+	case "user":
+	case "role":
+	// case "instance-profile":
+	default:
+		return nil, fmt.Errorf("unrecognized principal type: %q", entity.Type)
+	}
+
+	if entity.FriendlyName == "" {
+		return nil, fmt.Errorf("unrecognized arn: %q is missing the resource name", iamArn)
+	}
+
+	return &entity, nil
+}
+
+// CanonicalArn returns the canonical ARN for referring to an IAM entity
+func (p *ParsedArn) CanonicalArn() string {
+	entityType := p.Type
+	// canonicalize "assumed-role" into "role"
+	if entityType == "assumed-role" {
+		entityType = "role"
+	}
+	// Annoyingly, the assumed-role entity type doesn't have the Path of the role which was assumed
+	// So, we "canonicalize" it by just completely dropping the path. The other option would be to
+	// make an AWS API call to look up the role by FriendlyName, which introduces more complexity to
+	// code and test, and it also breaks backwards compatibility in an area where we would really want
+	// it
+	return fmt.Sprintf("arn:%s:iam::%s:%s/%s", p.Partition, p.AccountNumber, entityType, p.FriendlyName)
+}

internal/iamauth/responses/responses.go

@@ -0,0 +1,92 @@
+package responses
+
+import "encoding/xml"
+
+type GetCallerIdentityResponse struct {
+	XMLName                 xml.Name                  `xml:"GetCallerIdentityResponse"`
+	GetCallerIdentityResult []GetCallerIdentityResult `xml:"GetCallerIdentityResult"`
+	ResponseMetadata        []ResponseMetadata        `xml:"ResponseMetadata"`
+}
+
+type GetCallerIdentityResult struct {
+	Arn     string `xml:"Arn"`
+	UserId  string `xml:"UserId"`
+	Account string `xml:"Account"`
+}
+
+type ResponseMetadata struct {
+	RequestId string `xml:"RequestId"`
+}
+
+// IAMEntity is an interface for getting details from an IAM Role or User.
+type IAMEntity interface {
+	EntityPath() string
+	EntityArn() string
+	EntityName() string
+	EntityId() string
+	EntityTags() map[string]string
+}
+
+var _ IAMEntity = (*Role)(nil)
+var _ IAMEntity = (*User)(nil)
+
+type GetRoleResponse struct {
+	XMLName          xml.Name           `xml:"GetRoleResponse"`
+	GetRoleResult    []GetRoleResult    `xml:"GetRoleResult"`
+	ResponseMetadata []ResponseMetadata `xml:"ResponseMetadata"`
+}
+
+type GetRoleResult struct {
+	Role Role `xml:"Role"`
+}
+
+type Role struct {
+	Arn      string `xml:"Arn"`
+	Path     string `xml:"Path"`
+	RoleId   string `xml:"RoleId"`
+	RoleName string `xml:"RoleName"`
+	Tags     []Tag  `xml:"Tags"`
+}
+
+func (r *Role) EntityPath() string            { return r.Path }
+func (r *Role) EntityArn() string             { return r.Arn }
+func (r *Role) EntityName() string            { return r.RoleName }
+func (r *Role) EntityId() string              { return r.RoleId }
+func (r *Role) EntityTags() map[string]string { return tagsToMap(r.Tags) }
+
+type GetUserResponse struct {
+	XMLName          xml.Name           `xml:"GetUserResponse"`
+	GetUserResult    []GetUserResult    `xml:"GetUserResult"`
+	ResponseMetadata []ResponseMetadata `xml:"ResponseMetadata"`
+}
+
+type GetUserResult struct {
+	User User `xml:"User"`
+}
+
+type User struct {
+	Arn      string `xml:"Arn"`
+	Path     string `xml:"Path"`
+	UserId   string `xml:"UserId"`
+	UserName string `xml:"UserName"`
+	Tags     []Tag  `xml:"Tags"`
+}
+
+func (u *User) EntityPath() string            { return u.Path }
+func (u *User) EntityArn() string             { return u.Arn }
+func (u *User) EntityName() string            { return u.UserName }
+func (u *User) EntityId() string              { return u.UserId }
+func (u *User) EntityTags() map[string]string { return tagsToMap(u.Tags) }
+
+type Tag struct {
+	Key   string `xml:"Key"`
+	Value string `xml:"Value"`
+}
+
+func tagsToMap(tags []Tag) map[string]string {
+	result := map[string]string{}
+	for _, tag := range tags {
+		result[tag.Key] = tag.Value
+	}
+	return result
+}

internal/iamauth/responses/responses_test.go

@@ -0,0 +1,157 @@
+package responses
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestParseArn(t *testing.T) {
+	cases := map[string]struct {
+		arn    string
+		expArn *ParsedArn
+	}{
+		"assumed-role": {
+			arn: "arn:aws:sts::000000000000:assumed-role/my-role/session-name",
+			expArn: &ParsedArn{
+				Partition:     "aws",
+				AccountNumber: "000000000000",
+				Type:          "assumed-role",
+				Path:          "",
+				FriendlyName:  "my-role",
+				SessionInfo:   "session-name",
+			},
+		},
+		"role": {
+			arn: "arn:aws:iam::000000000000:role/my-role",
+			expArn: &ParsedArn{
+				Partition:     "aws",
+				AccountNumber: "000000000000",
+				Type:          "role",
+				Path:          "",
+				FriendlyName:  "my-role",
+				SessionInfo:   "",
+			},
+		},
+		"user": {
+			arn: "arn:aws:iam::000000000000:user/my-user",
+			expArn: &ParsedArn{
+				Partition:     "aws",
+				AccountNumber: "000000000000",
+				Type:          "user",
+				Path:          "",
+				FriendlyName:  "my-user",
+				SessionInfo:   "",
+			},
+		},
+		"role with path": {
+			arn: "arn:aws:iam::000000000000:role/path/my-role",
+			expArn: &ParsedArn{
+				Partition:     "aws",
+				AccountNumber: "000000000000",
+				Type:          "role",
+				Path:          "path",
+				FriendlyName:  "my-role",
+				SessionInfo:   "",
+			},
+		},
+		"role with path 2": {
+			arn: "arn:aws:iam::000000000000:role/path/to/my-role",
+			expArn: &ParsedArn{
+				Partition:     "aws",
+				AccountNumber: "000000000000",
+				Type:          "role",
+				Path:          "path/to",
+				FriendlyName:  "my-role",
+				SessionInfo:   "",
+			},
+		},
+		"role with path 3": {
+			arn: "arn:aws:iam::000000000000:role/some/path/to/my-role",
+			expArn: &ParsedArn{
+				Partition:     "aws",
+				AccountNumber: "000000000000",
+				Type:          "role",
+				Path:          "some/path/to",
+				FriendlyName:  "my-role",
+				SessionInfo:   "",
+			},
+		},
+		"user with path": {
+			arn: "arn:aws:iam::000000000000:user/path/my-user",
+			expArn: &ParsedArn{
+				Partition:     "aws",
+				AccountNumber: "000000000000",
+				Type:          "user",
+				Path:          "path",
+				FriendlyName:  "my-user",
+				SessionInfo:   "",
+			},
+		},
+
+		// Invalid cases
+		"empty string":               {arn: ""},
+		"wildcard":                   {arn: "*"},
+		"missing prefix":             {arn: ":aws:sts::000000000000:assumed-role/my-role/session-name"},
+		"missing partition":          {arn: "arn::sts::000000000000:assumed-role/my-role/session-name"},
+		"missing service":            {arn: "arn:aws:::000000000000:assumed-role/my-role/session-name"},
+		"missing separator":          {arn: "arn:aws:sts:000000000000:assumed-role/my-role/session-name"},
+		"missing account id":         {arn: "arn:aws:sts:::assumed-role/my-role/session-name"},
+		"missing resource":           {arn: "arn:aws:sts::000000000000:"},
+		"assumed-role missing parts": {arn: "arn:aws:sts::000000000000:assumed-role/my-role"},
+		"role missing parts":         {arn: "arn:aws:sts::000000000000:role"},
+		"role missing parts 2":       {arn: "arn:aws:sts::000000000000:role/"},
+		"user missing parts":         {arn: "arn:aws:sts::000000000000:user"},
+		"user missing parts 2":       {arn: "arn:aws:sts::000000000000:user/"},
+		"unsupported service":        {arn: "arn:aws:ecs:us-east-1:000000000000:task/my-task/00000000000000000000000000000000"},
+	}
+
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			parsed, err := ParseArn(c.arn)
+			if c.expArn != nil {
+				require.NoError(t, err)
+				require.Equal(t, c.expArn, parsed)
+			} else {
+				require.Error(t, err)
+				require.Nil(t, parsed)
+			}
+		})
+	}
+}
+
+func TestCanonicalArn(t *testing.T) {
+	cases := map[string]struct {
+		arn    string
+		expArn string
+	}{
+		"assumed-role arn": {
+			arn:    "arn:aws:sts::000000000000:assumed-role/my-role/session-name",
+			expArn: "arn:aws:iam::000000000000:role/my-role",
+		},
+		"role arn": {
+			arn:    "arn:aws:iam::000000000000:role/my-role",
+			expArn: "arn:aws:iam::000000000000:role/my-role",
+		},
+		"role arn with path": {
+			arn:    "arn:aws:iam::000000000000:role/path/to/my-role",
+			expArn: "arn:aws:iam::000000000000:role/my-role",
+		},
+		"user arn": {
+			arn:    "arn:aws:iam::000000000000:user/my-user",
+			expArn: "arn:aws:iam::000000000000:user/my-user",
+		},
+		"user arn with path": {
+			arn:    "arn:aws:iam::000000000000:user/path/to/my-user",
+			expArn: "arn:aws:iam::000000000000:user/my-user",
+		},
+	}
+
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			parsed, err := ParseArn(c.arn)
+			require.NoError(t, err)
+			require.Equal(t, c.expArn, parsed.CanonicalArn())
+		})
+	}
+}

internal/iamauth/responsestest/testing.go

@@ -0,0 +1,81 @@
+package responsestest
+
+import (
+	"strings"
+
+	"github.com/hashicorp/consul/internal/iamauth/responses"
+)
+
+func MakeGetCallerIdentityResponse(arn, userId, accountId string) responses.GetCallerIdentityResponse {
+	// Sanity check the UserId for unit tests.
+	parsed := parseArn(arn)
+	switch parsed.Type {
+	case "assumed-role":
+		if !strings.Contains(userId, ":") {
+			panic("UserId for assumed-role in GetCallerIdentity response must be '<uniqueId>:<session>'")
+		}
+	default:
+		if strings.Contains(userId, ":") {
+			panic("UserId in GetCallerIdentity must not contain ':'")
+		}
+	}
+
+	return responses.GetCallerIdentityResponse{
+		GetCallerIdentityResult: []responses.GetCallerIdentityResult{
+			{
+				Arn:     arn,
+				UserId:  userId,
+				Account: accountId,
+			},
+		},
+	}
+}
+
+func MakeGetRoleResponse(arn, id string, tags ...responses.Tag) responses.GetRoleResponse {
+	if strings.Contains(id, ":") {
+		panic("RoleId in GetRole response must not contain ':'")
+	}
+	parsed := parseArn(arn)
+	return responses.GetRoleResponse{
+		GetRoleResult: []responses.GetRoleResult{
+			{
+				Role: responses.Role{
+					Arn:      arn,
+					Path:     parsed.Path,
+					RoleId:   id,
+					RoleName: parsed.FriendlyName,
+					Tags:     tags,
+				},
+			},
+		},
+	}
+}
+
+func MakeGetUserResponse(arn, id string, tags ...responses.Tag) responses.GetUserResponse {
+	if strings.Contains(id, ":") {
+		panic("UserId in GetUser resposne must not contain ':'")
+	}
+	parsed := parseArn(arn)
+	return responses.GetUserResponse{
+		GetUserResult: []responses.GetUserResult{
+			{
+				User: responses.User{
+					Arn:      arn,
+					Path:     parsed.Path,
+					UserId:   id,
+					UserName: parsed.FriendlyName,
+					Tags:     tags,
+				},
+			},
+		},
+	}
+}
+
+func parseArn(arn string) *responses.ParsedArn {
+	parsed, err := responses.ParseArn(arn)
+	if err != nil {
+		// For testing, just fail immediately.
+		panic(err)
+	}
+	return parsed
+}

internal/iamauth/token.go

@@ -0,0 +1,343 @@
+package iamauth
+
+import (
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/textproto"
+	"net/url"
+	"strings"
+
+	"github.com/hashicorp/consul/lib/stringslice"
+)
+
+const (
+	amzHeaderPrefix    = "X-Amz-"
+	defaultIAMEndpoint = "https://iam.amazonaws.com"
+	defaultSTSEndpoint = "https://sts.amazonaws.com"
+)
+
+var defaultAllowedSTSRequestHeaders = []string{
+	"X-Amz-Algorithm",
+	"X-Amz-Content-Sha256",
+	"X-Amz-Credential",
+	"X-Amz-Date",
+	"X-Amz-Security-Token",
+	"X-Amz-Signature",
+	"X-Amz-SignedHeaders",
+}
+
+// BearerToken is a login "token" for an IAM auth method. It is a signed
+// sts:GetCallerIdentity request in JSON format. Optionally, it can include a
+// signed embedded iam:GetRole or iam:GetUser request in the headers.
+type BearerToken struct {
+	config *Config
+
+	getCallerIdentityMethod string
+	getCallerIdentityURL    string
+	getCallerIdentityHeader http.Header
+	getCallerIdentityBody   string
+
+	getIAMEntityMethod string
+	getIAMEntityURL    string
+	getIAMEntityHeader http.Header
+	getIAMEntityBody   string
+
+	entityRequestType       string
+	parsedCallerIdentityURL *url.URL
+	parsedIAMEntityURL      *url.URL
+}
+
+var _ json.Unmarshaler = (*BearerToken)(nil)
+
+func NewBearerToken(loginToken string, config *Config) (*BearerToken, error) {
+	token := &BearerToken{config: config}
+	if err := json.Unmarshal([]byte(loginToken), &token); err != nil {
+		return nil, fmt.Errorf("invalid token: %s", err)
+	}
+
+	if err := token.validate(); err != nil {
+		return nil, err
+	}
+
+	if config.EnableIAMEntityDetails {
+		method, err := token.getHeader(token.config.GetEntityMethodHeader)
+		if err != nil {
+			return nil, err
+		}
+
+		rawUrl, err := token.getHeader(token.config.GetEntityURLHeader)
+		if err != nil {
+			return nil, err
+		}
+
+		headerJson, err := token.getHeader(token.config.GetEntityHeadersHeader)
+		if err != nil {
+			return nil, err
+		}
+
+		var header http.Header
+		if err := json.Unmarshal([]byte(headerJson), &header); err != nil {
+			return nil, err
+		}
+
+		body, err := token.getHeader(token.config.GetEntityBodyHeader)
+		if err != nil {
+			return nil, err
+		}
+
+		parsedUrl, err := parseUrl(rawUrl)
+		if err != nil {
+			return nil, err
+		}
+
+		token.getIAMEntityMethod = method
+		token.getIAMEntityBody = body
+		token.getIAMEntityURL = rawUrl
+		token.getIAMEntityHeader = header
+		token.parsedIAMEntityURL = parsedUrl
+
+		reqType, err := token.validateIAMEntityBody()
+		if err != nil {
+			return nil, err
+		}
+		token.entityRequestType = reqType
+	}
+	return token, nil
+}
+
+// https://github.com/hashicorp/vault/blob/b17e3256dde937a6248c9a2fa56206aac93d07de/builtin/credential/aws/path_login.go#L1178
+func (t *BearerToken) validate() error {
+	if t.getCallerIdentityMethod != "POST" {
+		return fmt.Errorf("iam_http_request_method must be POST")
+	}
+	if err := t.validateGetCallerIdentityBody(); err != nil {
+		return err
+	}
+	if err := t.validateAllowedSTSHeaderValues(); err != nil {
+		return err
+	}
+	return nil
+}
+
+// https://github.com/hashicorp/vault/blob/b17e3256dde937a6248c9a2fa56206aac93d07de/builtin/credential/aws/path_login.go#L1439
+func (t *BearerToken) validateGetCallerIdentityBody() error {
+	allowedValues := url.Values{
+		"Action": []string{"GetCallerIdentity"},
+		// Will assume for now that future versions don't change
+		// the semantics
+		"Version": nil, // any value is allowed
+	}
+	if _, err := parseRequestBody(t.getCallerIdentityBody, allowedValues); err != nil {
+		return fmt.Errorf("iam_request_body error: %s", err)
+	}
+
+	return nil
+}
+
+func (t *BearerToken) validateIAMEntityBody() (string, error) {
+	allowedValues := url.Values{
+		"Action":   []string{"GetRole", "GetUser"},
+		"RoleName": nil, // any value is allowed
+		"UserName": nil,
+		"Version":  nil,
+	}
+	body, err := parseRequestBody(t.getIAMEntityBody, allowedValues)
+	if err != nil {
+		return "", fmt.Errorf("iam_request_headers[%s] error: %s", t.config.GetEntityBodyHeader, err)
+	}
+
+	// Disallow GetRole+UserName and GetUser+RoleName.
+	action := body["Action"][0]
+	_, hasRoleName := body["RoleName"]
+	_, hasUserName := body["UserName"]
+	if action == "GetUser" && hasUserName && !hasRoleName {
+		return action, nil
+	} else if action == "GetRole" && hasRoleName && !hasUserName {
+		return action, nil
+	}
+	return "", fmt.Errorf("iam_request_headers[%q] error: invalid request body %q", t.config.GetEntityBodyHeader, t.getIAMEntityBody)
+}
+
+// parseRequestBody parses the AWS STS or IAM request body, such as 'Action=GetRole&RoleName=my-role'.
+// It returns the parsed values, or an error if there are unexpected fields based on allowedValues.
+//
+// A key-value pair in the body is allowed if:
+//  - It is a single value (i.e. no bodies like 'Action=1&Action=2')
+//  - allowedValues[key] is an empty slice or nil (any value is allowed for the key)
+//  - allowedValues[key] is non-empty and contains the exact value
+// This always requires an 'Action' field is present and non-empty.
+func parseRequestBody(body string, allowedValues url.Values) (url.Values, error) {
+	qs, err := url.ParseQuery(body)
+	if err != nil {
+		return nil, err
+	}
+
+	// Action field is always required.
+	if _, ok := qs["Action"]; !ok || len(qs["Action"]) == 0 || qs["Action"][0] == "" {
+		return nil, fmt.Errorf(`missing field "Action"`)
+	}
+
+	// Ensure the body does not have extra fields and each
+	// field in the body matches the allowed values.
+	for k, v := range qs {
+		exp, ok := allowedValues[k]
+		if k != "Action" && !ok {
+			return nil, fmt.Errorf("unexpected field %q", k)
+		}
+
+		if len(exp) == 0 {
+			// empty indicates any value is okay
+			continue
+		} else if len(v) != 1 || !stringslice.Contains(exp, v[0]) {
+			return nil, fmt.Errorf("unexpected value %s=%v", k, v)
+		}
+	}
+
+	return qs, nil
+}
+
+// https://github.com/hashicorp/vault/blob/861454e0ed1390d67ddaf1a53c1798e5e291728c/builtin/credential/aws/path_config_client.go#L349
+func (t *BearerToken) validateAllowedSTSHeaderValues() error {
+	for k := range t.getCallerIdentityHeader {
+		h := textproto.CanonicalMIMEHeaderKey(k)
+		if strings.HasPrefix(h, amzHeaderPrefix) &&
+			!stringslice.Contains(defaultAllowedSTSRequestHeaders, h) &&
+			!stringslice.Contains(t.config.AllowedSTSHeaderValues, h) {
+			return fmt.Errorf("invalid request header: %s", h)
+		}
+	}
+	return nil
+}
+
+// UnmarshalJSON unmarshals the bearer token details which contains an HTTP
+// request (a signed sts:GetCallerIdentity request).
+func (t *BearerToken) UnmarshalJSON(data []byte) error {
+	var rawData struct {
+		Method        string `json:"iam_http_request_method"`
+		UrlBase64     string `json:"iam_request_url"`
+		HeadersBase64 string `json:"iam_request_headers"`
+		BodyBase64    string `json:"iam_request_body"`
+	}
+
+	if err := json.Unmarshal(data, &rawData); err != nil {
+		return err
+	}
+
+	rawUrl, err := base64.StdEncoding.DecodeString(rawData.UrlBase64)
+	if err != nil {
+		return err
+	}
+
+	headersJson, err := base64.StdEncoding.DecodeString(rawData.HeadersBase64)
+	if err != nil {
+		return err
+	}
+
+	var headers http.Header
+	// This is a JSON-string in JSON
+	if err := json.Unmarshal(headersJson, &headers); err != nil {
+		return err
+	}
+
+	body, err := base64.StdEncoding.DecodeString(rawData.BodyBase64)
+	if err != nil {
+		return err
+	}
+
+	t.getCallerIdentityMethod = rawData.Method
+	t.getCallerIdentityBody = string(body)
+	t.getCallerIdentityHeader = headers
+	t.getCallerIdentityURL = string(rawUrl)
+
+	parsedUrl, err := parseUrl(t.getCallerIdentityURL)
+	if err != nil {
+		return err
+	}
+	t.parsedCallerIdentityURL = parsedUrl
+	return nil
+}
+
+func parseUrl(s string) (*url.URL, error) {
+	u, err := url.Parse(s)
+	if err != nil {
+		return nil, err
+	}
+	// url.Parse doesn't error on empty string
+	if u == nil || u.Scheme == "" || u.Host == "" || u.Path == "" {
+		return nil, fmt.Errorf("url is invalid: %q", s)
+	}
+	return u, nil
+}
+
+// GetCallerIdentityRequest returns the sts:GetCallerIdentity request decoded
+// from the bearer token.
+func (t *BearerToken) GetCallerIdentityRequest() (*http.Request, error) {
+	// NOTE: We need to ensure we're calling STS, instead of acting as an unintended network proxy
+	// The protection against this is that this method will only call the endpoint specified in the
+	// client config (defaulting to sts.amazonaws.com), so it would require an admin to override
+	// the endpoint to talk to alternate web addresses
+	endpoint := defaultSTSEndpoint
+	if t.config.STSEndpoint != "" {
+		endpoint = t.config.STSEndpoint
+	}
+
+	return buildHttpRequest(
+		t.getCallerIdentityMethod,
+		endpoint,
+		t.parsedCallerIdentityURL,
+		t.getCallerIdentityBody,
+		t.getCallerIdentityHeader,
+	)
+}
+
+// GetEntityRequest returns the iam:GetUser or iam:GetRole request from the request details,
+// if present, embedded in the headers of the sts:GetCallerIdentity request.
+func (t *BearerToken) GetEntityRequest() (*http.Request, error) {
+	endpoint := defaultIAMEndpoint
+	if t.config.IAMEndpoint != "" {
+		endpoint = t.config.IAMEndpoint
+	}
+
+	return buildHttpRequest(
+		t.getIAMEntityMethod,
+		endpoint,
+		t.parsedIAMEntityURL,
+		t.getIAMEntityBody,
+		t.getIAMEntityHeader,
+	)
+}
+
+// getHeader returns the header from s.GetCallerIdentityHeader, or an error if
+// the header is not found or is not a single value.
+func (t *BearerToken) getHeader(name string) (string, error) {
+	values := t.getCallerIdentityHeader.Values(name)
+	if len(values) == 0 {
+		return "", fmt.Errorf("missing header %q", name)
+	}
+	if len(values) != 1 {
+		return "", fmt.Errorf("invalid value for header %q (expected 1 item)", name)
+	}
+	return values[0], nil
+}
+
+// buildHttpRequest returns an HTTP request from the given details.
+// This supports sending to a custom endpoint, but always preserves the
+// Host header and URI path, which are signed and cannot be modified.
+// There's a deeper explanation of this in the Vault source code.
+// https://github.com/hashicorp/vault/blob/b17e3256dde937a6248c9a2fa56206aac93d07de/builtin/credential/aws/path_login.go#L1569
+func buildHttpRequest(method, endpoint string, parsedUrl *url.URL, body string, headers http.Header) (*http.Request, error) {
+	targetUrl := fmt.Sprintf("%s%s", endpoint, parsedUrl.RequestURI())
+	request, err := http.NewRequest(method, targetUrl, strings.NewReader(body))
+	if err != nil {
+		return nil, err
+	}
+	request.Host = parsedUrl.Host
+	for k, vals := range headers {
+		for _, val := range vals {
+			request.Header.Add(k, val)
+		}
+	}
+	return request, nil
+}

internal/iamauth/token_test.go

@@ -0,0 +1,364 @@
+package iamauth
+
+import (
+	"net/http"
+	"net/url"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewBearerToken(t *testing.T) {
+	cases := map[string]struct {
+		tokenStr string
+		config   Config
+		expToken BearerToken
+		expError string
+	}{
+		"valid token": {
+			tokenStr: validBearerTokenJson,
+			expToken: validBearerTokenParsed,
+		},
+		"valid token with role": {
+			tokenStr: validBearerTokenWithRoleJson,
+			config: Config{
+				EnableIAMEntityDetails: true,
+				GetEntityMethodHeader:  "X-Consul-IAM-GetEntity-Method",
+				GetEntityURLHeader:     "X-Consul-IAM-GetEntity-URL",
+				GetEntityHeadersHeader: "X-Consul-IAM-GetEntity-Headers",
+				GetEntityBodyHeader:    "X-Consul-IAM-GetEntity-Body",
+			},
+			expToken: validBearerTokenWithRoleParsed,
+		},
+
+		"empty json": {
+			tokenStr: `{}`,
+			expError: "unexpected end of JSON input",
+		},
+		"missing iam_request_method field": {
+			tokenStr: tokenJsonMissingMethodField,
+			expError: "iam_http_request_method must be POST",
+		},
+		"missing iam_request_url field": {
+			tokenStr: tokenJsonMissingUrlField,
+			expError: "url is invalid",
+		},
+		"missing iam_request_headers field": {
+			tokenStr: tokenJsonMissingHeadersField,
+			expError: "unexpected end of JSON input",
+		},
+		"missing iam_request_body field": {
+			tokenStr: tokenJsonMissingBodyField,
+			expError: "iam_request_body error",
+		},
+		"invalid json": {
+			tokenStr: `{`,
+			expError: "unexpected end of JSON input",
+		},
+	}
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			token, err := NewBearerToken(c.tokenStr, &c.config)
+			t.Logf("token = %+v", token)
+			if c.expError != "" {
+				require.Error(t, err)
+				require.Contains(t, err.Error(), c.expError)
+				require.Nil(t, token)
+			} else {
+				require.NoError(t, err)
+				c.expToken.config = &c.config
+				require.Equal(t, &c.expToken, token)
+			}
+		})
+	}
+}
+
+func TestParseRequestBody(t *testing.T) {
+	cases := map[string]struct {
+		body          string
+		allowedValues url.Values
+		expValues     url.Values
+		expError      string
+	}{
+		"one allowed field": {
+			body:          "Action=GetCallerIdentity&Version=1234",
+			allowedValues: url.Values{"Version": []string{"1234"}},
+			expValues: url.Values{
+				"Action":  []string{"GetCallerIdentity"},
+				"Version": []string{"1234"},
+			},
+		},
+		"many allowed fields": {
+			body: "Action=GetRole&RoleName=my-role&Version=1234",
+			allowedValues: url.Values{
+				"Action":   []string{"GetUser", "GetRole"},
+				"UserName": nil,
+				"RoleName": nil,
+				"Version":  nil,
+			},
+			expValues: url.Values{
+				"Action":   []string{"GetRole"},
+				"RoleName": []string{"my-role"},
+				"Version":  []string{"1234"},
+			},
+		},
+		"action only": {
+			body:          "Action=GetRole",
+			allowedValues: nil,
+			expValues:     url.Values{"Action": []string{"GetRole"}},
+		},
+
+		"empty body": {
+			expValues: url.Values{},
+			expError:  `missing field "Action"`,
+		},
+		"disallowed field": {
+			body:          "Action=GetRole&Version=1234&Extra=Abc",
+			allowedValues: url.Values{"Action": nil, "Version": nil},
+			expError:      `unexpected field "Extra"`,
+		},
+		"mismatched action": {
+			body:          "Action=GetRole",
+			allowedValues: url.Values{"Action": []string{"GetUser"}},
+			expError:      `unexpected value Action=[GetRole]`,
+		},
+		"mismatched field": {
+			body:          "Action=GetRole&Extra=1234",
+			allowedValues: url.Values{"Action": nil, "Extra": []string{"abc"}},
+			expError:      `unexpected value Extra=[1234]`,
+		},
+		"multi-valued field": {
+			body:          "Action=GetRole&Action=GetUser",
+			allowedValues: url.Values{"Action": []string{"GetRole", "GetUser"}},
+			// only one value is allowed.
+			expError: `unexpected value Action=[GetRole GetUser]`,
+		},
+		"empty action": {
+			body:          "Action=",
+			allowedValues: nil,
+			expError:      `missing field "Action"`,
+		},
+		"missing action": {
+			body:          "Version=1234",
+			allowedValues: url.Values{"Action": []string{"GetRole"}},
+			expError:      `missing field "Action"`,
+		},
+	}
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			values, err := parseRequestBody(c.body, c.allowedValues)
+			if c.expError != "" {
+				require.Error(t, err)
+				require.Contains(t, err.Error(), c.expError)
+				require.Nil(t, values)
+			} else {
+				require.NoError(t, err)
+				require.Equal(t, c.expValues, values)
+			}
+		})
+	}
+}
+
+func TestValidateGetCallerIdentityBody(t *testing.T) {
+	cases := map[string]struct {
+		body     string
+		expError string
+	}{
+		"valid":   {"Action=GetCallerIdentity&Version=1234", ""},
+		"valid 2": {"Action=GetCallerIdentity", ""},
+		"empty action": {
+			"Action=",
+			`iam_request_body error: missing field "Action"`,
+		},
+		"invalid action": {
+			"Action=GetRole",
+			`iam_request_body error: unexpected value Action=[GetRole]`,
+		},
+		"missing action": {
+			"Version=1234",
+			`iam_request_body error: missing field "Action"`,
+		},
+		"empty": {
+			"",
+			`iam_request_body error: missing field "Action"`,
+		},
+	}
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			token := &BearerToken{getCallerIdentityBody: c.body}
+			err := token.validateGetCallerIdentityBody()
+			if c.expError != "" {
+				require.Error(t, err)
+				require.Contains(t, err.Error(), c.expError)
+			} else {
+				require.NoError(t, err)
+			}
+		})
+	}
+}
+
+func TestValidateIAMEntityBody(t *testing.T) {
+	cases := map[string]struct {
+		body       string
+		expReqType string
+		expError   string
+	}{
+		"valid role": {
+			body:       "Action=GetRole&RoleName=my-role&Version=1234",
+			expReqType: "GetRole",
+		},
+		"valid role without version": {
+			body:       "Action=GetRole&RoleName=my-role",
+			expReqType: "GetRole",
+		},
+		"valid user": {
+			body:       "Action=GetUser&UserName=my-role&Version=1234",
+			expReqType: "GetUser",
+		},
+		"valid user without version": {
+			body:       "Action=GetUser&UserName=my-role",
+			expReqType: "GetUser",
+		},
+
+		"invalid action": {
+			body:     "Action=GetCallerIdentity",
+			expError: `unexpected value Action=[GetCallerIdentity]`,
+		},
+		"role missing action": {
+			body:     "RoleName=my-role&Version=1234",
+			expError: `missing field "Action"`,
+		},
+		"user missing action": {
+			body:     "UserName=my-role&Version=1234",
+			expError: `missing field "Action"`,
+		},
+		"empty": {
+			body:     "",
+			expError: `missing field "Action"`,
+		},
+		"empty action": {
+			body:     "Action=",
+			expError: `missing field "Action"`,
+		},
+		"role with user name": {
+			body:     "Action=GetRole&UserName=my-role&Version=1234",
+			expError: `invalid request body`,
+		},
+		"user with role name": {
+			body:     "Action=GetUser&RoleName=my-role&Version=1234",
+			expError: `invalid request body`,
+		},
+	}
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			token := &BearerToken{
+				config:           &Config{},
+				getIAMEntityBody: c.body,
+			}
+			reqType, err := token.validateIAMEntityBody()
+			if c.expError != "" {
+				require.Error(t, err)
+				require.Contains(t, err.Error(), c.expError)
+				require.Equal(t, "", reqType)
+			} else {
+				require.NoError(t, err)
+				require.Equal(t, c.expReqType, reqType)
+			}
+		})
+	}
+}
+
+var (
+	validBearerTokenJson = `{
+  "iam_http_request_method":"POST",
+  "iam_request_body":"QWN0aW9uPUdldENhbGxlcklkZW50aXR5JlZlcnNpb249MjAxMS0wNi0xNQ==",
+  "iam_request_headers":"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",
+  "iam_request_url":"aHR0cHM6Ly9zdHMuYW1hem9uYXdzLmNvbS8="
+}`
+
+	validBearerTokenParsed = BearerToken{
+		getCallerIdentityMethod: "POST",
+		getCallerIdentityURL:    "https://sts.amazonaws.com/",
+		getCallerIdentityHeader: http.Header{
+			"Authorization":        []string{"AWS4-HMAC-SHA256 Credential=fake/20220322/us-east-1/sts/aws4_request, SignedHeaders=content-length;content-type;host;x-amz-date;x-amz-security-token, Signature=efc320b972d07b38b65eb24256805e03149da586d804f8c6364ce98debe080b1"},
+			"Content-Length":       []string{"43"},
+			"Content-Type":         []string{"application/x-www-form-urlencoded; charset=utf-8"},
+			"User-Agent":           []string{"aws-sdk-go/1.42.34 (go1.17.5; darwin; amd64)"},
+			"X-Amz-Date":           []string{"20220322T211103Z"},
+			"X-Amz-Security-Token": []string{"fake"},
+		},
+		getCallerIdentityBody: "Action=GetCallerIdentity&Version=2011-06-15",
+		parsedCallerIdentityURL: &url.URL{
+			Scheme: "https",
+			Host:   "sts.amazonaws.com",
+			Path:   "/",
+		},
+	}
+
+	validBearerTokenWithRoleJson = `{"iam_http_request_method":"POST","iam_request_body":"QWN0aW9uPUdldENhbGxlcklkZW50aXR5JlZlcnNpb249MjAxMS0wNi0xNQ==","iam_request_headers":"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","iam_request_url":"aHR0cDovLzEyNy4wLjAuMTo2MzY5Ni9zdHMv"}`
+
+	validBearerTokenWithRoleParsed = BearerToken{
+		getCallerIdentityMethod: "POST",
+		getCallerIdentityURL:    "http://127.0.0.1:63696/sts/",
+		getCallerIdentityHeader: http.Header{
+			"Authorization":                  []string{"AWS4-HMAC-SHA256 Credential=fake-key-id/20220322/fake-region/sts/aws4_request, SignedHeaders=content-length;content-type;host;x-amz-date;x-consul-iam-getentity-body;x-consul-iam-getentity-headers;x-consul-iam-getentity-method;x-consul-iam-getentity-url, Signature=561ac31b5ad01c124c54c168f76ea6bfd645b8ec5345f8357729c9aa0b471337"},
+			"Content-Length":                 []string{"43"},
+			"Content-Type":                   []string{"application/x-www-form-urlencoded; charset=utf-8"},
+			"User-Agent":                     []string{"aws-sdk-go/1.42.34 (go1.17.5; darwin; amd64)"},
+			"X-Amz-Date":                     []string{"20220322T225742Z"},
+			"X-Consul-Iam-Getentity-Body":    []string{"Action=GetRole&RoleName=my-role&Version=2010-05-08"},
+			"X-Consul-Iam-Getentity-Headers": []string{`{"Authorization":["AWS4-HMAC-SHA256 Credential=fake-key-id/20220322/us-east-1/iam/aws4_request, SignedHeaders=content-length;content-type;host;x-amz-date, Signature=aa2a19d0a305d74bbd009776bca880e53cfa991e483e403947181a41cc482940"],"Content-Length":["50"],"Content-Type":["application/x-www-form-urlencoded; charset=utf-8"],"User-Agent":["aws-sdk-go/1.42.34 (go1.17.5; darwin; amd64)"],"X-Amz-Date":["20220322T225742Z"]}`},
+			"X-Consul-Iam-Getentity-Method":  []string{"POST"},
+			"X-Consul-Iam-Getentity-Url":     []string{"https://iam.amazonaws.com/"},
+		},
+		getCallerIdentityBody: "Action=GetCallerIdentity&Version=2011-06-15",
+
+		// Fields parsed from headers above
+		getIAMEntityMethod: "POST",
+		getIAMEntityURL:    "https://iam.amazonaws.com/",
+		getIAMEntityHeader: http.Header{
+			"Authorization":  []string{"AWS4-HMAC-SHA256 Credential=fake-key-id/20220322/us-east-1/iam/aws4_request, SignedHeaders=content-length;content-type;host;x-amz-date, Signature=aa2a19d0a305d74bbd009776bca880e53cfa991e483e403947181a41cc482940"},
+			"Content-Length": []string{"50"},
+			"Content-Type":   []string{"application/x-www-form-urlencoded; charset=utf-8"},
+			"User-Agent":     []string{"aws-sdk-go/1.42.34 (go1.17.5; darwin; amd64)"},
+			"X-Amz-Date":     []string{"20220322T225742Z"},
+		},
+		getIAMEntityBody:  "Action=GetRole&RoleName=my-role&Version=2010-05-08",
+		entityRequestType: "GetRole",
+
+		parsedCallerIdentityURL: &url.URL{
+			Scheme: "http",
+			Host:   "127.0.0.1:63696",
+			Path:   "/sts/",
+		},
+		parsedIAMEntityURL: &url.URL{
+			Scheme: "https",
+			Host:   "iam.amazonaws.com",
+			Path:   "/",
+		},
+	}
+
+	tokenJsonMissingMethodField = `{
+  "iam_request_body":"QWN0aW9uPUdldENhbGxlcklkZW50aXR5JlZlcnNpb249MjAxMS0wNi0xNQ==",
+  "iam_request_headers":"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",
+  "iam_request_url":"aHR0cHM6Ly9zdHMuYW1hem9uYXdzLmNvbS8="
+}`
+
+	tokenJsonMissingBodyField = `{
+  "iam_http_request_method":"POST",
+  "iam_request_headers":"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",
+  "iam_request_url":"aHR0cHM6Ly9zdHMuYW1hem9uYXdzLmNvbS8="
+}`
+
+	tokenJsonMissingHeadersField = `{
+  "iam_http_request_method":"POST",
+  "iam_request_body":"QWN0aW9uPUdldENhbGxlcklkZW50aXR5JlZlcnNpb249MjAxMS0wNi0xNQ==",
+  "iam_request_url":"aHR0cHM6Ly9zdHMuYW1hem9uYXdzLmNvbS8="
+}`
+
+	tokenJsonMissingUrlField = `{
+  "iam_http_request_method":"POST",
+  "iam_request_body":"QWN0aW9uPUdldENhbGxlcklkZW50aXR5JlZlcnNpb249MjAxMS0wNi0xNQ==",
+  "iam_request_headers":"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"
+}`
+)

internal/iamauth/util.go

@@ -0,0 +1,158 @@
+package iamauth
+
+import (
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+
+	"github.com/aws/aws-sdk-go/aws"
+	"github.com/aws/aws-sdk-go/aws/credentials"
+	"github.com/aws/aws-sdk-go/aws/endpoints"
+	"github.com/aws/aws-sdk-go/aws/request"
+	"github.com/aws/aws-sdk-go/aws/session"
+	"github.com/aws/aws-sdk-go/service/iam"
+	"github.com/aws/aws-sdk-go/service/sts"
+	"github.com/hashicorp/consul/internal/iamauth/responses"
+	"github.com/hashicorp/go-hclog"
+)
+
+type LoginInput struct {
+	Creds            *credentials.Credentials
+	IncludeIAMEntity bool
+	STSEndpoint      string
+	STSRegion        string
+
+	Logger hclog.Logger
+
+	ServerIDHeaderValue string
+	// Customizable header names
+	ServerIDHeaderName     string
+	GetEntityMethodHeader  string
+	GetEntityURLHeader     string
+	GetEntityHeadersHeader string
+	GetEntityBodyHeader    string
+}
+
+// GenerateLoginData populates the necessary data to send for the bearer token.
+// https://github.com/hashicorp/go-secure-stdlib/blob/main/awsutil/generate_credentials.go#L232-L301
+func GenerateLoginData(in *LoginInput) (map[string]interface{}, error) {
+	cfg := aws.Config{
+		Credentials: in.Creds,
+		Region:      aws.String(in.STSRegion),
+	}
+	if in.STSEndpoint != "" {
+		cfg.Endpoint = aws.String(in.STSEndpoint)
+	} else {
+		cfg.EndpointResolver = endpoints.ResolverFunc(stsSigningResolver)
+	}
+
+	stsSession, err := session.NewSessionWithOptions(session.Options{Config: cfg})
+	if err != nil {
+		return nil, err
+	}
+
+	svc := sts.New(stsSession)
+	stsRequest, _ := svc.GetCallerIdentityRequest(nil)
+
+	// Include the iam:GetRole or iam:GetUser request in headers.
+	if in.IncludeIAMEntity {
+		entityRequest, err := formatSignedEntityRequest(svc, in)
+		if err != nil {
+			return nil, err
+		}
+
+		headersJson, err := json.Marshal(entityRequest.HTTPRequest.Header)
+		if err != nil {
+			return nil, err
+		}
+		requestBody, err := ioutil.ReadAll(entityRequest.HTTPRequest.Body)
+		if err != nil {
+			return nil, err
+		}
+
+		stsRequest.HTTPRequest.Header.Add(in.GetEntityMethodHeader, entityRequest.HTTPRequest.Method)
+		stsRequest.HTTPRequest.Header.Add(in.GetEntityURLHeader, entityRequest.HTTPRequest.URL.String())
+		stsRequest.HTTPRequest.Header.Add(in.GetEntityHeadersHeader, string(headersJson))
+		stsRequest.HTTPRequest.Header.Add(in.GetEntityBodyHeader, string(requestBody))
+	}
+
+	// Inject the required auth header value, if supplied, and then sign the request including that header
+	if in.ServerIDHeaderValue != "" {
+		stsRequest.HTTPRequest.Header.Add(in.ServerIDHeaderName, in.ServerIDHeaderValue)
+	}
+
+	stsRequest.Sign()
+
+	// Now extract out the relevant parts of the request
+	headersJson, err := json.Marshal(stsRequest.HTTPRequest.Header)
+	if err != nil {
+		return nil, err
+	}
+	requestBody, err := ioutil.ReadAll(stsRequest.HTTPRequest.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	return map[string]interface{}{
+		"iam_http_request_method": stsRequest.HTTPRequest.Method,
+		"iam_request_url":         base64.StdEncoding.EncodeToString([]byte(stsRequest.HTTPRequest.URL.String())),
+		"iam_request_headers":     base64.StdEncoding.EncodeToString(headersJson),
+		"iam_request_body":        base64.StdEncoding.EncodeToString(requestBody),
+	}, nil
+}
+
+// STS is a really weird service that used to only have global endpoints but now has regional endpoints as well.
+// For backwards compatibility, even if you request a region other than us-east-1, it'll still sign for us-east-1.
+// See, e.g., https://docs.aws.amazon.com/IAM/latest/UserGuide/id_credentials_temp_enable-regions.html#id_credentials_temp_enable-regions_writing_code
+// So we have to shim in this EndpointResolver to force it to sign for the right region
+func stsSigningResolver(service, region string, optFns ...func(*endpoints.Options)) (endpoints.ResolvedEndpoint, error) {
+	defaultEndpoint, err := endpoints.DefaultResolver().EndpointFor(service, region, optFns...)
+	if err != nil {
+		return defaultEndpoint, err
+	}
+	defaultEndpoint.SigningRegion = region
+	return defaultEndpoint, nil
+}
+
+func formatSignedEntityRequest(svc *sts.STS, in *LoginInput) (*request.Request, error) {
+	// We need to retrieve the IAM user or role for the iam:GetRole or iam:GetUser request.
+	// GetCallerIdentity returns this and requires no permissions.
+	resp, err := svc.GetCallerIdentity(nil)
+	if err != nil {
+		return nil, err
+	}
+
+	arn, err := responses.ParseArn(*resp.Arn)
+	if err != nil {
+		return nil, err
+	}
+
+	iamSession, err := session.NewSessionWithOptions(session.Options{
+		Config: aws.Config{
+			Credentials: svc.Config.Credentials,
+		},
+	})
+	if err != nil {
+		return nil, err
+	}
+	iamSvc := iam.New(iamSession)
+
+	var req *request.Request
+	switch arn.Type {
+	case "role", "assumed-role":
+		req, _ = iamSvc.GetRoleRequest(&iam.GetRoleInput{RoleName: &arn.FriendlyName})
+	case "user":
+		req, _ = iamSvc.GetUserRequest(&iam.GetUserInput{UserName: &arn.FriendlyName})
+	default:
+		return nil, fmt.Errorf("entity %s is not an IAM role or IAM user", arn.Type)
+	}
+
+	// Inject the required auth header value, if supplied, and then sign the request including that header
+	if in.ServerIDHeaderValue != "" {
+		req.HTTPRequest.Header.Add(in.ServerIDHeaderName, in.ServerIDHeaderValue)
+	}
+
+	req.Sign()
+	return req, nil
+}

lib/glob.go

@@ -0,0 +1,24 @@
+package lib
+
+import "strings"
+
+// GlobbedStringsMatch compares item to val with support for a leading and/or
+// trailing wildcard '*' in item.
+func GlobbedStringsMatch(item, val string) bool {
+	if len(item) < 2 {
+		return val == item
+	}
+
+	hasPrefix := strings.HasPrefix(item, "*")
+	hasSuffix := strings.HasSuffix(item, "*")
+
+	if hasPrefix && hasSuffix {
+		return strings.Contains(val, item[1:len(item)-1])
+	} else if hasPrefix {
+		return strings.HasSuffix(val, item[1:])
+	} else if hasSuffix {
+		return strings.HasPrefix(val, item[:len(item)-1])
+	}
+
+	return val == item
+}

lib/glob_test.go

@@ -0,0 +1,37 @@
+package lib
+
+import "testing"
+
+func TestGlobbedStringsMatch(t *testing.T) {
+	tests := []struct {
+		item   string
+		val    string
+		expect bool
+	}{
+		{"", "", true},
+		{"*", "*", true},
+		{"**", "**", true},
+		{"*t", "t", true},
+		{"*t", "test", true},
+		{"t*", "test", true},
+		{"*test", "test", true},
+		{"*test", "a test", true},
+		{"test", "a test", false},
+		{"*test", "tests", false},
+		{"test*", "test", true},
+		{"test*", "testsss", true},
+		{"test**", "testsss", false},
+		{"test**", "test*", true},
+		{"**test", "*test", true},
+		{"TEST", "test", false},
+		{"test", "test", true},
+	}
+
+	for _, tt := range tests {
+		actual := GlobbedStringsMatch(tt.item, tt.val)
+
+		if actual != tt.expect {
+			t.Fatalf("Bad testcase %#v, expected %t, got %t", tt, tt.expect, actual)
+		}
+	}
+}