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Tier 3 — Production

Tier 3 produces verifiable releases — a third party can confirm what built each artifact, with which inputs, from which commit, and that the artifact hasn’t been tampered with since. This is the level at which a downstream consumer can meaningfully audit you without re-running your build.

You should be cleanly on Tier 2 — Hardened before adopting Tier 3. Tier 3 patterns assume the Tier 1–2 disciplines are in place; some (3.1, 3.4, 3.5) won’t function correctly without them.

Patterns

Section titled “Patterns”
  1. Generate SLSA Build L3 provenance for every release — slsa-framework/slsa-github-generator reusable workflow, sigstore-signed attestation, verifier-friendly subjects
  2. Generate and attach an SBOM at release time — CycloneDX or SPDX, per-language tooling, checksum sidecar
  3. Sign release artifacts with sigstore / cosign (keyless) — OIDC-rooted signatures, no long-lived private keys, transparency-log-backed
  4. Use OIDC for cloud and registry pushes — federated trust replacing static API keys for AWS / GCP / Azure / npm / PyPI Trusted Publishers
  5. Publish with registry-native provenance — npm publish --provenance, PyPI PEP 740 attestations, crates.io trusted publishing
  6. Publish an OpenSSF Scorecard score — automated posture rollup, badged in the README, public on scorecard.dev
  7. Protect the default branch and release tags with rulesets — JSON-defined, source-controlled, including signature requirements and tag-update blocks

Worked example

Section titled “Worked example”

Ozark-Security-Labs/SessionScope is the most mature Tier 3 release pipeline in the OSL portfolio: tag-protection check, multi-platform build, reproducible-build verification (cold + warm, byte-identical), CycloneDX SBOM, SLSA generic_slsa3 provenance via sigstore, checksum sidecars for every artifact, CHANGELOG-extracted release notes — all stitched together with explicit needs: dependencies between jobs.

Ozark-Security-Labs/PkgWarden demonstrates the branch-protection-ruleset side (Rule 3.7) cleanly: .github/rulesets/main-protection.json committed in the repo, applied to the default branch with signed commits required and the repository hygiene status check gating merges.

Three patterns currently lack an in-tree OSL real example and link to canonical external references instead:

  • Rule 3.3 (cosign signed artifacts) — no OSL project uses standalone cosign sign-blob today; SLSA provenance covers most of the same trust surface via its sigstore-signed attestation
  • Rule 3.4 (OIDC for cloud / registry) — no OSL release pipeline federates to a cloud provider today
  • Rule 3.5 (registry-native provenance) — no OSL npm publish flow uses --provenance today; the osl-* TypeScript forks predate npm Trusted Publishers

Closing those gaps is a near-term follow-up; the underlying infrastructure (sigstore via SLSA, id-token: write already in workflows) is mostly in place.

After Tier 3

Section titled “After Tier 3”

Tier 3 is the recommended terminal state for production OSS. Beyond it lies:

  • Reproducible builds — covered briefly in Rule 3.1’s “going further” section; SessionScope demonstrates the in-CI verification pattern (F-26)
  • Full SLSA Build L4 — adds hermetic builds, isolated builders. Currently impractical for most projects without dedicated infrastructure
  • Ecosystem-specific deeper hardening — out of scope for this guide