Attest and verify a container image with GitHub Artifact Attestations

Steps

1. In a GitHub Actions workflow, build and push the container image to a registry; record the image digest (sha256:...) from the push step output.
2. Add a step using the actions/attest-build-provenance action, passing subject-name (the full image reference) and subject-digest (the digest without the sha256: prefix) to generate a signed SLSA provenance attestation.
3. The attestation is automatically stored in the GitHub attestation store and signed using the workflow's OIDC identity via Sigstore's keyless signing—no secrets required.
4. To verify, run gh attestation verify oci://<image-reference>@<digest> --owner <github-org> on a machine with the GitHub CLI installed; the command fetches the attestation from GitHub and validates the Sigstore signature.
5. To verify an SBOM or other non-provenance predicate type, pass --predicate-type <predicate-uri> to gh attestation verify explicitly, as the default predicate is SLSA provenance.
6. In private or internal repositories, artifact attestations require a GitHub Enterprise Cloud plan; for public repositories, attestations are available on all plan tiers.