open-vault/website/source/docs/auth/gcp.html.md

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docs	Auth Plugin Backend: GCP	docs-auth-gcp	The gcp backend plugin allows automated authentication of AWS entities.

Auth Plugin Backend: gcp

The gcp plugin backend allows authentication against Vault using Google credentials. It treats GCP as a Trusted Third Party and expects a JSON Web Token (JWT) signed by Google credentials from the authenticating entity. This token can be generated through different GCP APIs depending on the type of entity.

Currently supports authentication for:

• GCP IAM service accounts (iam)

We will update the documentation as we introduce more supported entities.

The following documentation assumes that the backend has been mounted at auth/gcp.

~> Note: The gcp backend is implemented as a Vault plugin backend. You must be using Vault v0.8.0+ to use plugins.

Authentication Workflow

IAM

The Vault authentication workflow for IAM service accounts is as follows:

1. A client with IAM service account credentials generates a signed JWT using the IAM projects.serviceAccounts.signJwt method. See usage for the expected format and example code.
2. The client sends this JWT to Vault in a login request with a role name. This role should have type iam
3. Vault grabs the kid header value, which contains the ID of the key-pair used to generate the JWT, and the sub ID/email to find the service account key. If the service account does not exist or the key is not linked to the service account, Vault will deny authentication.
4. Vault authorizes the confirmed service account against the given role. See authorization section to see how each type of role handles authorization.

The iam Authentication Token

The expected format of the JWT payload is as follows:

{
  "sub" : "[SERVICE ACCOUNT IDENTIFIER]",
  "aud" : "vault/[ROLE NAME]",
  "exp" : "[EXPIRATION]",
}

• [SERVICE ACCOUNT ID OR EMAIL]: Either the email or the unique ID of a service account.
• [ROLE NAME]: Name of the role that this token will be used to login against. The full expected aud string should be "vault/$roleName".
• [EXPIRATION] : A NumericDate value (seconds from Epoch). This value must be before the max JWT expiration allowed for a role (see max_jwt_exp parameter for creating a role). This defaults to 15 minutes and cannot be more than a hour.

Note: By default, we enforce a shorter exp period than the default length for a given token (1 hour) in order to make reuse of tokens difficult. You can customize this value for a given role but it will be capped at an hour.

To generate this token, we use the Google IAM API method.

HTTP Request Example

This uses Google API HTTP annotation. Note the $PAYLOAD must be a marshaled JSON string with escaped double quotes.

curl -H "Authorization: Bearer $OAUTH_TOKEN" \
    -H "Content-Type: application/json" \
    -X POST -d '{"payload":"'$PAYLOAD'"}' https://iam.googleapis.com/v1/projects/$PROJECT/serviceAccounts/$SERVICE_ACCOUNT:signJwt

Golang Example

We use the Go OAuth2 libraries, GCP IAM API, and Vault API.

// Abbreviated imports to show libraries.
import (
	vaultapi "github.com/hashicorp/vault/api"
	"golang.org/x/oauth2"
	"golang.org/x/oauth2/google"
	"google.golang.org/api/iam/v1"
	...
)

func main() {
	// Start [PARAMS]
	project := "project-123456"
	serviceAccount := "myserviceaccount@project-123456.iam.gserviceaccount.com"
	credsPath := "path/to/creds.json"

	os.Setenv("VAULT_ADDR", "https://vault.mycompany.com")
	defer os.Setenv("VAULT_ADDR", "")
	// End [PARAMS]

	// Start [GCP IAM Setup]
	jsonBytes, err := ioutil.ReadFile(credsPath)
	if err != nil {
		log.Fatal(err)
	}
	config, err := google.JWTConfigFromJSON(jsonBytes, iam.CloudPlatformScope)
	if err != nil {
		log.Fatal(err)
	}

	httpClient := config.Client(oauth2.NoContext)
	iamClient, err := iam.New(httpClient)
	if err != nil {
		log.Fatal(err)
	}
	// End [GCP IAM Setup]

	// 1. Generate signed JWT using IAM.
	resourceName := fmt.Sprintf("projects/%s/serviceAccounts/%s", project, serviceAccount)
	jwtPayload := map[string]interface{}{
		"aud": "auth/gcp/login",
		"sub": serviceAccount,
		"exp": time.Now().Add(time.Minute * 10).Unix(),
	}

	payloadBytes, err := json.Marshal(jwtPayload)
	if err != nil {
		log.Fatal(err)
	}
	signJwtReq := &iam.SignJwtRequest{
		Payload: string(payloadBytes),
	}

	resp, err := iamClient.Projects.ServiceAccounts.SignJwt(resourceName, signJwtReq).Do()
	if err != nil {
		log.Fatal(err)
	}

	// 2. Send signed JWT in login request to Vault.
	vaultClient, err := vaultapi.NewClient(vaultapi.DefaultConfig())
	if err != nil {
		log.Fatal(err)
	}

	vaultResp, err := vaultClient.Logical().Write(
		"auth/gcp/login",
		map[string]interface{}{
			"role": "test",
			"jwt":  resp.SignedJwt,
	})

	if err != nil {
		log.Fatal(err)
	}

	// 3. Use auth token from response.
	log.Println("Access token: %s", vaultResp.Auth.ClientToken)
	vaultClient.SetToken(vaultResp.Auth.ClientToken)
	// ...
}

Authorization Workflow

For gcp, login is per-role. Each role has a specific set of restrictions that an authorized entity must fit in order to login. These restrictions are specific to the role type.

Currently supported role types are:

• iam

Vault validates an authenticated entity against the role and uses the role to determine information about the lease, including Vault policies assigned and TTLs. For a full list of accepted arguments, see role API docs.

About iam Roles

iam roles support the following role restrictions:

• service_accounts: A list of service accounts that are allowed to login as this role. This list accepts either service account IDs or emails.

Note: In the future we hope to support restrictions related to IAM policies/permissions. With current IAM APIs, querying all IAM roles or permissions (set or inherited) on an entity is very difficult to do and overall ends with not a great story. We plan to wait until more functionality is supported before attempting to add permission-based constraints.

Plugin Backend

~> Note: The following section is only relevant if you decide to enable the gcp backend as an external plugin. The gcp plugin backend is integrated into Vault as a builtin backend by default.

Plugin Setup

Assuming you have saved the binary vault-plugin-auth-gcp to some folder and configured the plugin directory for your server at path/to/plugins:

# Write plugin to catalog
$ vault write sys/plugins/catalog/gcp-auth command='vault-plugin-auth-gcp' sha_256=<sha-256-of-the-binary>
Success! Data written to: sys/plugins/catalog/gcp-auth

# Enable plugin backend for auth.
$ vault auth-enable -path=gcp -plugin-name=gcp-auth plugin
Successfully mounted plugin 'plugin' at 'gcp'!

Contributing

This plugin is developed in a separate Github repository: hashicorp/vault-plugin-auth-gcp. Please file all feature requests, bugs, and pull requests specific to the GCP plugin under that repository.

Authentication

Via the CLI

Enable GCP authentication in Vault

$ vault auth-enable gcp

Configure the GCP authentication backend

$ vault write auth/gcp/config credentials=@path/to/creds.json

Configuration: This includes GCP credentials Vault will use these to make calls to GCP APIs. If credentials are not configured or if the user explicitly sets the config with no credentials, the Vault server will attempt to use Application Default Credentials as set on the Vault server.

See API documentation to learn more about parameters.

Create a role

$ vault write auth/gcp/role/dev-role \
    type="iam" \
    project_id="project-123456" \
    policies="prod,dev" \
    service_accounts="serviceaccount1@project1234.iam.gserviceaccount.com,uuid123,..."
    ...

Roles: Roles are associated with an authentication type/entity and a set of Vault policies. Roles are configured with constraints specific to the authentication type, as well as overall constraints and configuration for the generated auth tokens.

We also expose a helper path for updating the service accounts attached to an existing iam role.

vault write auth/gcp/role/dev-role/add-service-accounts \
  values='serviceAccountToAdd,...'

vault write auth/gcp/role/dev-role/delete-service-accounts \
    values='serviceAccountToRemove,...' \
  ...

See API docs to view parameters for role creation and updates.

Login to get a Vault Token

Once the backend is setup and roles are registered with the backend, the user can login against a specific role.

$ vault write auth/gcp/login role='dev-role' jwt='eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...'

The role and jwt parameters are required. These map to the name of the role to login against, and the signed JWT token for authenticating a role respectively. The format of the provided JWT differs depending on the authenticating entity.

Via the API

Enable GCP authentication in Vault

$ curl $VAULT_ADDR/v1/sys/auth/gcp -d '{ "type": "gcp" }'

Configure the GCP authentication backend

$ curl $VAULT_ADDR/v1/auth/gcp/config \
-d '{  "credentials": "{...}" }'

Create a role

$ curl $VAULT_ADDR/v1/auth/gcp/role/dev-role \
-d '{ "type": "iam", "project_id": "project-123456", ...}'

Login to get a Vault Token

The endpoint for the GCP login is auth/gcp/login.

The gcp mountpoint value in the url is the default mountpoint value. If you have mounted the gcp backend with a different mountpoint, use that value.

The role and jwt should be sent in the POST body encoded as JSON.

$ curl $VAULT_ADDR/v1/auth/gcp/login \
    -d '{ "role": "dev-role", "jwt": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9..." }'

The response will be in JSON. For example:

{
    "auth":{
        "client_token":"f33f8c72-924e-11f8-cb43-ac59d697597c",
        "accessor":"0e9e354a-520f-df04-6867-ee81cae3d42d",
        "policies":[
            "default",
            "dev",
            "prod"
        ],
        "metadata":{
            "role": "dev-role",
            "service_account_email": "dev1@project-123456.iam.gserviceaccount.com",
            "service_account_id": "111111111111111111111"
        },
        "lease_duration":2764800,
        "renewable":true
    },
    ...
}

API

The GCP Auth Plugin has a full HTTP API. Please see the API docs for more details.