--- layout: docs page_title: Google Cloud - Auth Methods description: |- The "gcp" auth method allows users and machines to authenticate to Vault using Google Cloud service accounts. --- # Google Cloud Auth Method The `gcp` auth method allows Google Cloud Platform entities to authenticate to Vault. Vault treats Google Cloud as a trusted third party and verifies authenticating entities against the Google Cloud APIs. This backend allows for authentication of: - Google Cloud IAM service accounts - Google Compute Engine (GCE) instances This backend focuses on identities specific to Google _Cloud_ and does not support authenticating arbitrary Google or Google Workspace users or generic OAuth against Google. This plugin is developed in a separate GitHub repository at [hashicorp/vault-plugin-auth-gcp][repo], but is automatically bundled in Vault releases. Please file all feature requests, bugs, and pull requests specific to the GCP plugin under that repository. ## Authenticate ### Via the CLI Helper Vault includes a CLI helper that obtains a signed JWT locally and sends the request to Vault. This helper is only available for IAM-type roles. ```shell-session $ vault login -method=gcp \ role="my-role" \ service_account="authenticating-account@my-project.iam.gserviceaccount.com" \ jwt_exp="15m" \ credentials=@path/to/signer/credentials.json ``` For more usage information, run `vault auth help gcp`. -> **Note:** The `project` parameter has been removed in Vault 1.5.9+, 1.6.5+, and 1.7.2+. It is no longer needed for configuration and will be ignored if provided. ### Via the CLI ```shell-session $ vault write -field=token auth/gcp/login \ role="my-role" \ jwt="eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9..." ``` See [Generating JWTs](#generating-jwts) for ways to obtain the JWT token. ### Via the API ```shell-session $ curl \ --request POST \ --data '{"role":"my-role", "jwt":"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9..."}' \ http://127.0.0.1:8200/v1/auth/gcp/login ``` See [API docs][api-docs] for expected response. ## Configuration Auth methods must be configured in advance before users or machines can authenticate. These steps are usually completed by an operator or configuration management tool. 1. Enable the Google Cloud auth method: ```text $ vault auth enable gcp ``` 1. Configure the auth method credentials: ```text $ vault write auth/gcp/config \ credentials=@/path/to/credentials.json ``` If you are using instance credentials or want to specify credentials via an environment variable, you can skip this step. To learn more, see the [Google Cloud Authentication](#authentication) section below. 1. Create a named role: For an `iam`-type role: ```text $ vault write auth/gcp/role/my-iam-role \ type="iam" \ policies="dev,prod" \ bound_service_accounts="my-service@my-project.iam.gserviceaccount.com" ``` For a `gce`-type role: ```text $ vault write auth/gcp/role/my-gce-role \ type="gce" \ policies="dev,prod" \ bound_projects="my-project1,my-project2" \ bound_zones="us-east1-b" \ bound_labels="foo:bar,zip:zap" \ bound_service_accounts="my-service@my-project.iam.gserviceaccount.com" ``` Note that `bound_service_accounts` is only required for `iam`-type roles. For the complete list of configuration options for each type, please see the [API documentation][api-docs]. ## Authentication The Google Cloud Vault auth method uses the official Google Cloud Golang SDK. This means it supports the common ways of [providing credentials to Google Cloud][cloud-creds]. 1. The environment variable `GOOGLE_APPLICATION_CREDENTIALS`. This is specified as the **path** to a Google Cloud credentials file, typically for a service account. If this environment variable is present, the resulting credentials are used. If the credentials are invalid, an error is returned. 1. Default instance credentials. When no environment variable is present, the default service account credentials are used. For more information on service accounts, please see the [Google Cloud Service Accounts documentation][service-accounts]. To use this auth method, the service account must have the following minimum scope: ```text https://www.googleapis.com/auth/cloud-platform ``` ### Required GCP Permissions #### Vault Server Permissions **For `iam`-type Vault roles**, Vault can be given the following roles: ```text roles/iam.serviceAccountKeyAdmin ``` **For `gce`-type Vault roles**, Vault can be given the following roles: ```text roles/compute.viewer ``` If you instead wish to create a custom role with only the exact GCP permissions required, use the following list of permissions: ```text iam.serviceAccounts.get iam.serviceAccountKeys.get compute.instances.get compute.instanceGroups.list ``` These allow Vault to: - verify the service account, either directly authenticating or associated with authenticating GCE instance, exists - get the corresponding public keys for verifying JWTs signed by service account private keys. - verify authenticating GCE instances exist - compare bound fields for GCE roles (zone/region, labels, or membership in given instance groups) If you are using Group Aliases as described below, you will also need to add the `resourcemanager.projects.get` permission. #### Permissions For Authenticating Against Vault Note that the previously mentioned permissions are given to the _Vault servers_. The IAM service account or GCE instance that is **authenticating against Vault** must have the following role: ```text roles/iam.serviceAccountTokenCreator ``` !> **WARNING:** Make sure this role is only applied so your service account can impersonate itself. If this role is applied GCP project-wide, this will allow the service account to impersonate any service account in the GCP project where it resides. See [Managing service account impersonation](https://cloud.google.com/iam/docs/impersonating-service-accounts) for more information. ## Group Aliases As of Vault 1.0, roles can specify an `add_group_aliases` boolean parameter that adds [group aliases][identity-group-aliases] to the auth response. These aliases can aid in building reusable policies since they are available as interpolated values in Vault's policy engine. Once enabled, the auth response will include the following aliases: ```json [ "project-$PROJECT_ID", "folder-$SUBFOLDER_ID", "folder-$FOLDER_ID", "organization-$ORG_ID" ] ``` If you are using a custom role for Vault server, you will need to add the `resourcemanager.projects.get` permission to your custom role. ## Implementation Details This section describes the implementation details for how Vault communicates with Google Cloud to authenticate and authorize JWT tokens. This information is provided for those who are curious, but these details are not required knowledge for using the auth method. ### IAM Login IAM login applies only to roles of type `iam`. The Vault authentication workflow for IAM service accounts looks like this: [![Vault Google Cloud IAM Login Workflow](/img/vault-gcp-iam-auth-workflow.svg)](/img/vault-gcp-iam-auth-workflow.svg) 1. The client generates a signed JWT using the Service Account Credentials [`projects.serviceAccounts.signJwt`][signjwt-method] API method. For examples of how to do this, see the [Generating JWTs](#generating-jwts) section. 2. The client sends this signed JWT to Vault along with a role name. 3. Vault extracts 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 denies authentication. 4. Vault authorizes the confirmed service account against the given role. If that is successful, a Vault token with the proper policies is returned. ### GCE Login GCE login only applies to roles of type `gce` and **must be completed on an instance running in GCE**. These steps will not work from your local laptop or another cloud provider. [![Vault Google Cloud GCE Login Workflow](/img/vault-gcp-gce-auth-workflow.svg)](/img/vault-gcp-gce-auth-workflow.svg) 1. The client obtains an [instance identity metadata token][instance-identity] on a GCE instance. 2. The client sends this JWT to Vault along with a role name. 3. Vault extracts the `kid` header value, which contains the ID of the key-pair used to generate the JWT, to find the OAuth2 public cert to verify this JWT. 4. Vault authorizes the confirmed instance against the given role, ensuring the instance matches the bound zones, regions, or instance groups. If that is successful, a Vault token with the proper policies is returned. ## Generating JWTs This section details the various methods and examples for obtaining JWT tokens. ### Service Account Credentials API This describes how to use the GCP Service Account Credentials [API method][signjwt-method] directly to generate the signed JWT with the claims that Vault expects. Note the CLI does this process for you and is much easier, and that there is very little reason to do this yourself. #### curl Example Vault requires the following minimum claim set: ```json { "sub": "$SERVICE_ACCOUNT_EMAIL_OR_ID", "aud": "vault/$ROLE", "exp": "$EXPIRATION" } ``` For the API method, providing the expiration claim `exp` is required. If it is omitted, it will not be added automatically and Vault will deny authentication. Expiration must be specified as a [NumericDate](https://tools.ietf.org/html/rfc7519#section-2) value (seconds from Epoch). This value must be before the max JWT expiration allowed for a role. This defaults to 15 minutes and cannot be more than 1 hour. One you have all this information, the JWT token can be signed using curl and [oauth2l](https://github.com/google/oauth2l): ```text ROLE="my-role" SERVICE_ACCOUNT="service-account@my-project.iam.gserviceaccount.com" OAUTH_TOKEN="$(oauth2l header cloud-platform)" EXPIRATION="" JWT_CLAIM="{\\\"aud\\\":\\\"vault/${ROLE}\\\", \\\"sub\\\": \\\"${SERVICE_ACCOUNT}\\\", \\\"exp\\\": ${EXPIRATION}}" curl \ --header "${OAUTH_TOKEN}" \ --header "Content-Type: application/json" \ --request POST \ --data "{\"payload\": \"${JWT_CLAIM}\"}" \ "https://iamcredentials.googleapis.com/v1/projects/-/serviceAccounts/${SERVICE_ACCOUNT}:signJwt" ``` #### gcloud Example You can also do this through the (currently beta) gcloud command. Note that you will be required to provide the expiration claim `exp` as a part of the JWT input to the command. ```shell-session $ gcloud beta iam service-accounts sign-jwt $INPUT_JWT_CLAIMS $OUTPUT_JWT_FILE \ --iam-account=service-account@my-project.iam.gserviceaccount.com \ --project=my-project ``` #### Golang Example Read more on the [Google Open Source blog](https://opensource.googleblog.com/2017/08/hashicorp-vault-and-google-cloud-iam.html). ### GCE GCE tokens **can only be generated from a GCE instance**. The JWT token can be obtained from the `service-accounts/default/identity` endpoint for a instance's metadata server. #### curl Example ```text ROLE="my-gce-role" curl \ --header "Metadata-Flavor: Google" \ --get \ --data-urlencode "audience=http://vault/${ROLE}" \ --data-urlencode "format=full" \ "http://metadata/computeMetadata/v1/instance/service-accounts/default/identity" ``` ## API The GCP Auth Plugin has a full HTTP API. Please see the [API docs][api-docs] for more details. [jwt]: https://tools.ietf.org/html/rfc7519 [signjwt-method]: https://cloud.google.com/iam/docs/reference/credentials/rest/v1/projects.serviceAccounts/signJwt [cloud-creds]: https://cloud.google.com/docs/authentication/production#providing_credentials_to_your_application [service-accounts]: https://cloud.google.com/compute/docs/access/service-accounts [api-docs]: /api-docs/auth/gcp [identity-group-aliases]: /api-docs/secret/identity/group-alias [instance-identity]: https://cloud.google.com/compute/docs/instances/verifying-instance-identity [repo]: https://github.com/hashicorp/vault-plugin-auth-gcp ## Code Example The following code snippet demonstrates the Google Cloud auth method to authenticate with Vault. ```go package main import ( "context" "fmt" "os" vault "github.com/hashicorp/vault/api" auth "github.com/hashicorp/vault/api/auth/gcp" ) // Fetches a key-value secret (kv-v2) after authenticating to Vault // via GCP IAM, one of two auth methods used to authenticate with // GCP (the other is GCE auth). func getSecretWithGCPAuthIAM() (string, error) { config := vault.DefaultConfig() // modify for more granular configuration client, err := vault.NewClient(config) if err != nil { return "", fmt.Errorf("unable to initialize Vault client: %w", err) } // For IAM-style auth, the environment variable GOOGLE_APPLICATION_CREDENTIALS // must be set with the path to a valid credentials JSON file, otherwise // Vault will fall back to Google's default instance credentials. // Learn about authenticating to GCS with service account credentials at https://cloud.google.com/docs/authentication/production if pathToCreds := os.Getenv("GOOGLE_APPLICATION_CREDENTIALS"); pathToCreds == "" { fmt.Printf("WARNING: Environment variable GOOGLE_APPLICATION_CREDENTIALS was not set. IAM client for JWT signing and Vault server IAM client will both fall back to default instance credentials.\n") } svcAccountEmail := fmt.Sprintf("%s@%s.iam.gserviceaccount.com", os.Getenv("GCP_SERVICE_ACCOUNT_NAME"), os.Getenv("GOOGLE_CLOUD_PROJECT")) // We pass the auth.WithIAMAuth option to use the IAM-style authentication // of the GCP auth backend. Otherwise, we default to using GCE-style // authentication, which gets its credentials from the metadata server. gcpAuth, err := auth.NewGCPAuth( "dev-role-iam", auth.WithIAMAuth(svcAccountEmail), ) if err != nil { return "", fmt.Errorf("unable to initialize GCP auth method: %w", err) } authInfo, err := client.Auth().Login(context.TODO(), gcpAuth) if err != nil { return "", fmt.Errorf("unable to login to GCP auth method: %w", err) } if authInfo == nil { return "", fmt.Errorf("login response did not return client token") } // get secret secret, err := client.Logical().Read("kv-v2/data/creds") if err != nil { return "", fmt.Errorf("unable to read secret: %w", err) } data, ok := secret.Data["data"].(map[string]interface{}) if !ok { return "", fmt.Errorf("data type assertion failed: %T %#v", secret.Data["data"], secret.Data["data"]) } // data map can contain more than one key-value pair, // in this case we're just grabbing one of them key := "password" value, ok := data[key].(string) if !ok { return "", fmt.Errorf("value type assertion failed: %T %#v", data[key], data[key]) } return value, nil } ``` ```cs using System; using System.Collections.Generic; using System.IO; using System.Threading.Tasks; using Google.Apis.Auth.OAuth2; using Google.Apis.Services; using Google.Apis.Iam.v1; using Newtonsoft.Json; using VaultSharp; using VaultSharp.V1.AuthMethods; using VaultSharp.V1.AuthMethods.GoogleCloud; using VaultSharp.V1.Commons; using Data = Google.Apis.Iam.v1.Data; namespace Examples { public class GCPAuthExample { /// /// Fetches a key-value secret (kv-v2) after authenticating to Vault via GCP IAM, /// one of two auth methods used to authenticate with GCP (the other is GCE auth). /// public string GetSecretGcp() { var vaultAddr = Environment.GetEnvironmentVariable("VAULT_ADDR"); if(String.IsNullOrEmpty(vaultAddr)) { throw new System.ArgumentNullException("Vault Address"); } var roleName = Environment.GetEnvironmentVariable("VAULT_ROLE"); if(String.IsNullOrEmpty(roleName)) { throw new System.ArgumentNullException("Vault Role Name"); } // Learn about authenticating to GCS with service account credentials at https://cloud.google.com/docs/authentication/production if(String.IsNullOrEmpty(Environment.GetEnvironmentVariable("GOOGLE_APPLICATION_CREDENTIALS"))) { Console.WriteLine("WARNING: Environment variable GOOGLE_APPLICATION_CREDENTIALS was not set. IAM client for JWT signing will fall back to default instance credentials."); } var jwt = SignJWT(); IAuthMethodInfo authMethod = new GoogleCloudAuthMethodInfo(roleName, jwt); var vaultClientSettings = new VaultClientSettings(vaultAddr, authMethod); IVaultClient vaultClient = new VaultClient(vaultClientSettings); // We can retrieve the secret after creating our VaultClient object Secret kv2Secret = null; kv2Secret = vaultClient.V1.Secrets.KeyValue.V2.ReadSecretAsync(path: "/creds").Result; var password = kv2Secret.Data.Data["password"]; return password.ToString(); } /// /// Generate signed JWT from GCP IAM /// private string SignJWT() { var roleName = Environment.GetEnvironmentVariable("GCP_ROLE"); var svcAcctName = Environment.GetEnvironmentVariable("GCP_SERVICE_ACCOUNT_NAME"); var gcpProjName = Environment.GetEnvironmentVariable("GOOGLE_CLOUD_PROJECT"); IamService iamService = new IamService(new BaseClientService.Initializer { HttpClientInitializer = GetCredential(), ApplicationName = "Google-iamSample/0.1", }); string svcEmail = $"{svcAcctName}@{gcpProjName}.iam.gserviceaccount.com"; string name = $"projects/-/serviceAccounts/{svcEmail}"; TimeSpan currentTime = (DateTime.UtcNow - new DateTime(1970, 1, 1)); int expiration = (int)(currentTime.TotalSeconds) + 900; Data.SignJwtRequest requestBody = new Data.SignJwtRequest(); requestBody.Payload = JsonConvert.SerializeObject(new Dictionary () { { "aud", $"vault/{roleName}" } , { "sub", svcEmail } , { "exp", expiration } }); ProjectsResource.ServiceAccountsResource.SignJwtRequest request = iamService.Projects.ServiceAccounts.SignJwt(requestBody, name); Data.SignJwtResponse response = request.Execute(); return JsonConvert.SerializeObject(response.SignedJwt).Replace("\"", ""); } public static GoogleCredential GetCredential() { GoogleCredential credential = Task.Run(() => GoogleCredential.GetApplicationDefaultAsync()).Result; if (credential.IsCreateScopedRequired) { credential = credential.CreateScoped("https://www.googleapis.com/auth/cloud-platform"); } return credential; } } } ```