Add Artifact Attestations to Workflow

Add SLSA build-provenance attestations to existing GitHub Actions workflows for Docker container images.

Steps

0. Find existing workflow files in .github/workflows/ that contain docker/build-push-action or similar steps. Note that composite actions may be used — read both the composite action and the calling workflow simultaneously.

1. Enable OIDC & Attestations permissions
   In each workflow's top-level permissions: block, grant both the OIDC token and attestations write privileges:

   permissions:
     id-token: write
     attestations: write
     contents: read       # (existing)
     packages: write      # (existing)

2. Log in to container registries
   Ensure authentication steps exist for each registry you'll attest against. Judge whether there are omissions based on the implemented content, rather than always logging into all registries.

   - name: Login to GHCR
     uses: docker/login-action@v3
     with:
       registry: ghcr.io
       username: ${{ github.actor }}
       password: ${{ secrets.GITHUB_TOKEN }}
   
   - name: Login to Docker Hub
     uses: docker/login-action@v3
     with:
       registry: index.docker.io
       username: ${{ secrets.DOCKERHUB_USERNAME }}
       password: ${{ secrets.DOCKERHUB_TOKEN }}
   
   - name: Login to Quay
     uses: docker/login-action@v3
     with:
       registry: quay.io
       username: ${{ secrets.QUAY_USERNAME }}
       password: ${{ secrets.QUAY_TOKEN }}

3. Build & push image, capturing the digest
   Use docker/build-push-action@v* with an id to reference its output. Judge tags based on implemented content.

   - name: Build and push image
     id: build_push
     uses: docker/build-push-action@v5
     with:
       context: .
       push: true
       tags: |
         ghcr.io/${{ github.repository }}:latest
         index.docker.io/${{ secrets.DOCKERHUB_USERNAME }}/your-repo:latest
         quay.io/${{ github.repository_owner }}/your-repo:latest

4. Add attestation steps
   After the build_push step, insert one actions/attest-build-provenance@v3 invocation per registry. The subject-name is the full image name without a tag. The subject-digest comes from the build step's output. Judge which registries to use based on implemented content.

   - name: Attest GHCR image
     uses: actions/attest-build-provenance@v3
     with:
       subject-name: ghcr.io/${{ github.repository }}
       subject-digest: ${{ steps.build_push.outputs.digest }}
   
   - name: Attest Docker Hub image
     uses: actions/attest-build-provenance@v3
     with:
       subject-name: index.docker.io/${{ secrets.DOCKERHUB_USERNAME }}/your-repo
       subject-digest: ${{ steps.build_push.outputs.digest }}
   
   - name: Attest Quay image
     uses: actions/attest-build-provenance@v3
     with:
       subject-name: quay.io/${{ github.repository_owner }}/your-repo
       subject-digest: ${{ steps.build_push.outputs.digest }}

5. Commit changes
   Write the git commit message in English.

   git add .github/workflows/docker_publish.yml # or whatever files you modified
   git commit --signoff -m "ci: add build-provenance attestations for container images"

6. Ask the user to push
   Tell the user to manually push the changes and verify attestations are created successfully. DO NOT perform a git push.