Trusted Publishers

Format

Trusted publishers are defined using the ALLOWED_PUBLISHERS environment variable. Each entry follows the format:

owner/repo:workflow.yml

Multiple entries are comma-separated:

ALLOWED_PUBLISHERS="my-org/frontend:deploy.yml,my-org/backend:publish.yaml"

How matching works

When a GitHub Actions workflow pushes an image, the OIDC token contains a job_workflow_ref claim like:

my-org/frontend/.github/workflows/deploy.yml@refs/heads/main

trupu extracts:

• repository: my-org/frontend (from the repository claim)
• workflow: deploy.yml (filename from job_workflow_ref)

Both must match an entry in ALLOWED_PUBLISHERS for the push to be authorized.

Restricting by ref

Optionally restrict which git refs (branches/tags) are allowed:

ALLOWED_REFS="refs/heads/main,refs/tags/v*"

When empty (default), any ref is accepted.

Security considerations

• Always specify the exact workflow filename — this prevents other workflows in the same repo from pushing
• Use ALLOWED_REFS to restrict pushes to release branches or tags
• Each trusted publisher entry is an AND condition: both repository and workflow must match
• The OIDC token is verified against GitHub’s JWKS endpoint, ensuring it was issued by GitHub and hasn’t been tampered with