Steps to authenticate to GCP within a GitHub Action

authenticate-to-gcp-steps.yml

# [...] your github action
      - name: Set up Google Cloud SDK
        uses: google-github-actions/setup-gcloud@v1
        with:
          project_id: ${{ secrets.GCP_PROJECT_ID }}
          export_default_credentials: true

      - name: Authenticate to GCP
        env:
          GCP_CREDENTIALS: ${{ secrets.GCP_CREDENTIALS }}
        run: |
          echo "$GCP_CREDENTIALS" | base64 --decode > "$HOME"/gcp-key.json
          gcloud auth activate-service-account --key-file="$HOME"/gcp-key.json
# [...] the rest of the action