Assume we want to deploy a CloudRun service to a GCP project from GitHub Action. GitHub needs to be authorized with GCP. We can generate the JSON key of a service account (that has sufficient IAM roles) and store it in the Github Repo as Secrets. Then we use this Service Account key to call GCP APIs. => It’s hazardous (in case that key is leaked).

But fortunately, GCP has a safer way to implement the same thing using Workload Identity Federation.

Workload Identity Federation workflow

1. Create a Workload Identity Pool

A Workload Identity Pool is used to manage external identities outside the GCP environment. The following command will create a new pool named: github-wif-pool

gcloud iam workload-identity-pools create github-wif-pool \
--location="global" --project=PROJECT-ID

2. Create a Workload Identity Pool Provider

A Workload Identity Pool Provider describes the relationship between Google Cloud and an external Identity Provider (IdP). In this article, the IdP is GitHub OIDC Provider. GCP IAM uses a token of the GitHub OIDC provider to authorize the permission on GCP resources.

gcloud iam workload-identity-pools providers create-oidc githubwif \
--location="global" --workload-identity-pool="github-wif-pool" \
--issuer-uri="https://token.actions.githubusercontent.com" \
--attribute-mapping="attribute.actor=assertion.actor,google.subject=assertion.sub,attribute.repository=assertion.repository" \
--project=PROJECT-ID

3. Service Account and IAMs

For example, we’ll use this service account SA-NAME@PROJECT-ID.iam.gserviceaccount.com with sufficient permission to deploy a CloudRun service. Workload Identiy Provider impersonates the service account.

We need to grant the role roles/iam.workloadIdentityUser to the above service account.

If we only allow IAM to authen the request coming from a specific Github repository your-github-username/your-repo

gcloud iam service-accounts add-iam-policy-binding SA-NAME@PROJECT-ID.iam.gserviceaccount.com \
--project=PROJECT-ID \
--role="roles/iam.workloadIdentityUser" \
--member="principalSet://iam.googleapis.com/projects/PROJECT-NUMBER/locations/global/workloadIdentityPools/github-wif-pool/attribute.repository/your-github-username/your-repo"

4. Step Google Auth on GitHub Action workflow file

Now, we can enable keyless authentication from GitHub Actions to GCP resources by defining this step in the workflow file.

- name: Google Auth
  id: auth
  uses: 'google-github-actions/auth@v1'
  with:
    token_format: 'access_token'
    workload_identity_provider: 'projects/PROJECT-NUMBER/locations/global/workloadIdentityPools/github-wif-pool/providers/githubwif'
    service_account: 'SA-NAME@PROJECT-ID.iam.gserviceaccount.com'

That’s all. Thanks for reading!