Generate SLSA provenance for a container image build in GitHub Actions using the slsa-framework/slsa-github-generator and verify the attestation with cosign
domain: slsa.dev · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
In your GitHub Actions workflow, build the container image and capture its digest (not just tag) as a workflow output using docker inspect or buildx build --metadata-file
Add a separate job that calls the slsa-framework/slsa-github-generator reusable workflow (.github/workflows/generator_container_slsa3.yml) with the image digest as an input
Grant the provenance job the 'id-token: write' permission so the generator can request an OIDC token for keyless signing via Sigstore Fulcio
The generator job produces a signed SLSA provenance attestation and attaches it to the image in the registry as an OCI artifact
Verify the attestation by running 'cosign verify-attestation --type slsaprovenance <image>@<digest>' against the registry and confirm the provenance matches the expected builder and source
Known gotchas
The image digest must be the exact SHA256 digest of the pushed image; using a mutable tag instead of a digest causes the provenance verification to fail because the tag may point to a different image later
The slsa-github-generator reusable workflow must run in an isolated job with no other steps; adding custom steps to the provenance job invalidates the SLSA level 3 guarantees
Provenance verification with cosign requires the registry to support OCI referrers; registries that do not support the referrers API will not return the attestation, causing verification to fail silently
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