auth

This GitHub Action establishes authentication to Google Cloud. It supports traditional authentication via a Google Cloud Service Account Key JSON and authentication via Workload Identity Federation.

Workload Identity Federation is the recommended approach as it obviates the need to export a long-lived Google Cloud service account key and establishes a trust delegation relationship between a particular GitHub Actions workflow invocation and permissions on Google Cloud.

With Service Account Key JSON

Create a Google Cloud service account and grant IAM permissions
Export the long-lived JSON service account key
Upload the JSON service account key to a GitHub secret

With Workload Identity Federation

Create a Google Cloud service account and grant IAM permissions
Create and configure a Workload Identity Provider for GitHub
Exchange the GitHub Actions OIDC token for a short-lived Google Cloud access token

Prerequisites

For authenticating via Google Cloud Service Account Keys, you must create an export a Google Cloud Service Account Key in JSON format.
For authenticating via Workload Identity Federation, you must create and configure a Google Cloud Workload Identity Provider. See setup for instructions.

Usage

jobs:
  job_id:
    # ...

    # Add "id-token" with the intended permissions.
    permissions:
      contents: 'read'
      id-token: 'write'

    steps:
    - id: 'auth'
      name: 'Authenticate to Google Cloud'
      uses: 'google-github-actions/auth@v0.4.0'
      with:
        token_format: 'access_token'
        workload_identity_provider: 'projects/123456789/locations/global/workloadIdentityPools/my-pool/providers/my-provider'
        service_account: 'my-service-account@my-project.iam.gserviceaccount.com'

    # Example of using the token:
    - name: 'Access secret'
      run: |-
        curl https://secretmanager.googleapis.com/v1/projects/my-project/secrets/my-secret/versions/1:access \
          --header "Authorization: Bearer ${{ steps.auth.outputs.access_token }}"

Note that changing the permissions block may remove some default permissions. See the permissions documentation for more information.

See Examples for more examples.

Inputs

Authenticating via Workload Identity Federation

The following inputs are for authenticating to Google Cloud via Workload Identity Federation.

workload_identity_provider: (Required) The full identifier of the Workload Identity Provider, including the project number, pool name, and provider name. If provided, this must be the full identifier which includes all parts:
```
projects/123456789/locations/global/workloadIdentityPools/my-pool/providers/my-provider
```
service_account: (Required) Email address or unique identifier of the Google Cloud service account for which to generate credentials. For example:
```
my-service-account@my-project.iam.gserviceaccount.com
```
audience: (Optional) The value for the audience (aud) parameter in the generated GitHub Actions OIDC token. This value defaults to the value of workload_identity_provider, which is also the default value Google Cloud expects for the audience parameter on the token. We do not recommend changing this value.

Authenticating via Service Account Key JSON

The following inputs are for authenticating to Google Cloud via a Service Account Key JSON. We recommend using Workload Identity Federation instead as exporting a long-lived Service Account Key JSON credential poses a security risk.

credentials_json: (Required) The Google Cloud JSON service account key to use for authentication. To generate access tokens or ID tokens using this service account, you must grant the underlying service account roles/iam.serviceAccountTokenCreator permissions on itself.

Generating OAuth 2.0 access tokens

The following inputs are for generating OAuth 2.0 access tokens for authenticating to Google Cloud as an output for use in future steps in the workflow.

token_format: This value must be "access_token" to generate OAuth 2.0 access tokens. To skip token generation, omit or set to the empty string "".
access_token_lifetime: (Optional) Desired lifetime duration of the access token, in seconds. This must be specified as the number of seconds with a trailing "s" (e.g. 30s). The default value is 1 hour (3600s).
access_token_scopes: (Optional) List of OAuth 2.0 access scopes to be included in the generated token. This is only valid when "token_format" is "access_token". The default value is:
```
https://www.googleapis.com/auth/cloud-platform
```

Generating ID tokens

The following inputs are for generating ID tokens for authenticating to Google Cloud as an output for use in future steps in the workflow.

token_format: This value must be "id_token" to generate ID tokens. To skip token generation, omit or set to the empty string "".
id_token_audience: (Required) The audience for the generated ID Token.
id_token_include_email: (Optional) Optional parameter of whether to include the service account email in the generated token. If true, the token will contain "email" and "email_verified" claims. This is only valid when "token_format" is "id_token". The default value is false.

Other inputs

The following inputs are for controlling the behavior of this GitHub Actions, regardless of the authentication mechanism.

project_id: (Optional) Custom project ID to use for authentication and exporting into other steps. If unspecified, the project ID will be extracted from the Workload Identity Provider or the Service Account Key JSON.
create_credentials_file: (Optional) If true, the action will securely generate a credentials file which can be used for authentication via gcloud and Google Cloud SDKs in other steps in the workflow. The default is true.
delegates: (Optional) List of additional service account emails or unique identities to use for impersonation in the chain. By default there are no delegates.

Outputs

project_id: Provided or extracted value for the Google Cloud project ID.
credentials_file_path: Path on the local filesystem where the generated credentials file resides. This is only available if "create_credentials_file" was set to true.
access_token: The Google Cloud access token for calling other Google Cloud APIs. This is only available when "token_format" is "access_token".
access_token_expiration: The RFC3339 UTC "Zulu" format timestamp for the access token. This is only available when "token_format" is "access_token".
id_token: The Google Cloud ID token. This is only available when "token_format" is "id_token".

Examples

Authenticating via Workload Identity Federation

This example demonstrates authenticating via Workload Identity Federation. For more information on how to setup and configure Workload Identity Federation, see #setup.

jobs:
  job_id:
    # ...

    # Add "id-token" with the intended permissions.
    permissions:
      contents: 'read'
      id-token: 'write'

    steps:
    - id: 'auth'
      name: 'Authenticate to Google Cloud'
      uses: `google-github-actions/auth@v0.4.0'
      with:
        workload_identity_provider: 'projects/123456789/locations/global/workloadIdentityPools/my-pool/providers/my-provider'
        service_account: 'my-service-account@my-project.iam.gserviceaccount.com'

Authenticating via Service Account Key JSON

This example demonstrates authenticating via a Google Cloud Service Account Key JSON. We recommend using Workload Identity Federation instead as exporting a long-lived Service Account Key JSON credential poses a security risk.

This example assumes you have created a GitHub Secret named 'GOOGLE_CREDENTIALS' with the contents being an export Google Cloud Service Account Key JSON. See Creating and managing Google Cloud Service Account Keys for more information.

jobs:
  job_id:
    # ...

    steps:
    - id: 'auth'
      name: 'Authenticate to Google Cloud'
      uses: `google-github-actions/auth@v0.4.0'
      with:
        credentials_json: '${{ secrets.GOOGLE_CREDENTIALS }}'

Configuring gcloud

This example demonstrates using this GitHub Action to configure authentication for the gcloud CLI tool. Note this does NOT work for the gsutil tool.

jobs:
  job_id:
    # ...

    # Add "id-token" with the intended permissions.
    permissions:
      contents: 'read'
      id-token: 'write'

    steps:
    # Install gcloud, do not specify authentication.
    - uses: 'google-github-actions/setup-gcloud@master'
      with:
        project_id: 'my-project'

    # Configure Workload Identity Federation via a credentials file.
    - id: 'auth'
      name: 'Authenticate to Google Cloud'
      uses: 'google-github-actions/auth@v0.4.0'
      with:
        workload_identity_provider: 'projects/123456789/locations/global/workloadIdentityPools/my-pool/providers/my-provider'
        service_account: 'my-service-account@my-project.iam.gserviceaccount.com'

    # Authenticate using the created credentials file.
    #
    # WARNING: The --cred-file flag is in preview and is subject to change.
    - id: 'gcloud'
      name: 'gcloud'
      run: |-
        gcloud auth login --brief --cred-file="${{ steps.auth.outputs.credentials_file_path }}"

        # Now you can run gcloud commands authenticated as the impersonated service account.
        gcloud secrets versions access "latest" --secret "my-secret"

Generating an OAuth 2.0 Access Token

This example demonstrates using this GitHub Action to generate an OAuth 2.0 Access Token for authenticating to Google Cloud. Most Google Cloud APIs accept this access token as authentication.

The default lifetime is 1 hour, but you can request up to 12 hours if you set the constraints/iam.allowServiceAccountCredentialLifetimeExtension organization policy.

Note: If you authenticate via credentials_json, the service account must have roles/iam.serviceAccountTokenCreator on itself.

jobs:
  job_id:
    # ...

    # Add "id-token" with the intended permissions.
    permissions:
      contents: 'read'
      id-token: 'write'

    steps:
    # Configure Workload Identity Federation and generate an access token.
    - id: 'auth'
      name: 'Authenticate to Google Cloud'
      uses: 'google-github-actions/auth@v0.4.0'
      with:
        token_format: 'access_token'
        workload_identity_provider: 'projects/123456789/locations/global/workloadIdentityPools/my-pool/providers/my-provider'
        service_account: 'my-service-account@my-project.iam.gserviceaccount.com'
        access_token_lifetime: '300s' # optional, default: '3600s' (1 hour)

    # Example of using the output. The token is usually provided as a Bearer
    # token.
    - id: 'access-secret'
      run: |-
        curl https://secretmanager.googleapis.com/v1/projects/my-project/secrets/my-secret/versions/1:access \
          --header "Authorization: Bearer ${{ steps.auth.outputs.access_token }}"

Generating an ID Token (JWT)

This example demonstrates using this GitHub Action to generate a Google Cloud ID Token for authenticating to Google Cloud. This is most commonly used when invoking a Cloud Run service.

Note: If you authenticate via credentials_json, the service account must have roles/iam.serviceAccountTokenCreator on itself.

jobs:
  job_id:
    # ...

    # Add "id-token" with the intended permissions.
    permissions:
      contents: 'read'
      id-token: 'write'

    steps:
    # Configure Workload Identity Federation and generate an access token.
    - id: 'auth'
      name: 'Authenticate to Google Cloud'
      uses: 'google-github-actions/auth@v0.4.0'
      with:
        token_format: 'access_token'
        workload_identity_provider: 'projects/123456789/locations/global/workloadIdentityPools/my-pool/providers/my-provider'
        service_account: 'my-service-account@my-project.iam.gserviceaccount.com'
        id_token_audience: 'https://myapp-uvehjacqzq.a.run.app' # required, value depends on target
        id_token_include_email: true # optional

    # Example of using the output. The token is usually provided as a Bearer
    # token.
    - id: 'invoke-service'
      run: |-
        curl https://myapp-uvehjacqzq.a.run.app \
          --header "Authorization: Bearer ${{ steps.auth.outputs.id_token }}"

Setting up Workload Identity Federation

To exchange a GitHub Actions OIDC token for a Google Cloud access token, you must create and configure a Workload Identity Provider. These instructions use the gcloud command-line tool.

Create or use an existing Google Cloud project. You must have privileges to create Workload Identity Pools, Workload Identity Providers, and to manage Service Accounts and IAM permissions. Save your project ID as an environment variable. The rest of these steps assume this environment variable is set:
```
export PROJECT_ID="my-project" # update with your value
```
(Optional) Create a Google Cloud Service Account. If you already have a Service Account, take note of the email address and skip this step.
```
gcloud iam service-accounts create "my-service-account" \
  --project "${PROJECT_ID}"
```
(Optional) Grant the Google Cloud Service Account permissions to access Google Cloud resources. This step varies by use case. For demonstration purposes, you could grant access to a Google Secret Manager secret or Google Cloud Storage object.

Enable the IAM Credentials API:

gcloud services enable iamcredentials.googleapis.com \
  --project "${PROJECT_ID}"

Create a Workload Identity Pool:

gcloud iam workload-identity-pools create "my-pool" \
  --project="${PROJECT_ID}" \
  --location="global" \
  --display-name="Demo pool"

Get the full ID of the Workload Identity Pool:

gcloud iam workload-identity-pools describe "my-pool" \
  --project="${PROJECT_ID}" \
  --location="global" \
  --format="value(name)"

Save this value as an environment variable:

export WORKLOAD_IDENTITY_POOL_ID="..." # value from above

Create a Workload Identity Provider in that pool:

gcloud iam workload-identity-pools providers create-oidc "my-provider" \
  --project="${PROJECT_ID}" \
  --location="global" \
  --workload-identity-pool="my-pool" \
  --display-name="Demo provider" \
  --attribute-mapping="google.subject=assertion.sub,attribute.actor=assertion.actor,attribute.aud=assertion.aud" \
  --issuer-uri="https://token.actions.githubusercontent.com"

The attribute mappings map claims in the GitHub Actions JWT to assertions you can make about the request (like the repository or GitHub username of the principal invoking the GitHub Action). These can be used to further restrict the authentication using --attribute-condition flags.

For example, you can map the attribute repository values (which can be used later to restrict the authentication to specific repositories):

--attribute-mapping="google.subject=assertion.sub,attribute.repository=assertion.repository"

Allow authentications from the Workload Identity Provider to impersonate the Service Account created above:

Warning: This grants access to any resource in the pool (all GitHub repos). It's strongly recommended that you map to a specific attribute such as the actor or repository name instead. See mapping external identities for more information.

gcloud iam service-accounts add-iam-policy-binding "my-service-account@${PROJECT_ID}.iam.gserviceaccount.com" \
  --project="${PROJECT_ID}" \
  --role="roles/iam.workloadIdentityUser" \
  --member="principalSet://iam.googleapis.com/${WORKLOAD_IDENTITY_POOL_ID}/*"

To map to a specific repository:

gcloud iam service-accounts add-iam-policy-binding "my-service-account@${PROJECT_ID}.iam.gserviceaccount.com" \
  --role="roles/iam.workloadIdentityUser" \
  --member="principalSet://iam.googleapis.com/${WORKLOAD_IDENTITY_POOL_ID}/attribute.repository/username/repo"

Use this GitHub Action with the Workload Identity Provider ID and Service Account email. The GitHub Action will mint a GitHub OIDC token and exchange the GitHub token for a Google Cloud access token (assuming the authorization is correct). This all happens without exporting a Google Cloud service account key JSON!

Note: It can take up to 5 minutes from when you configure the Workload Identity Pool mapping until the permissions are available.

GitHub Token Format

Here is a sample GitHub Token for reference for attribute mappings:

{
  "jti": "...",
  "sub": "repo:username/reponame:ref:refs/heads/master",
  "aud": "https://iam.googleapis.com/projects/123456789/locations/global/workloadIdentityPools/my-pool/providers/my-provider",
  "ref": "refs/heads/master",
  "sha": "d11880f4f451ee35192135525dc974c56a3c1b28",
  "repository": "username/reponame",
  "repository_owner": "reponame",
  "run_id": "1238222155",
  "run_number": "18",
  "run_attempt": "1",
  "actor": "username",
  "workflow": "OIDC",
  "head_ref": "",
  "base_ref": "",
  "event_name": "push",
  "ref_type": "branch",
  "job_workflow_ref": "username/reponame/.github/workflows/token.yml@refs/heads/master",
  "iss": "https://token.actions.githubusercontent.com",
  "nbf": 1631718827,
  "exp": 1631719727,
  "iat": 1631719427
}

License

cysiv/auth

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