I'm raising this as a potential enhancement/addition to current set of X.509 extensions used by Sigstore when encapsulating GitHub Actions OIDC claims, based on this comment in the pre-RFC discussion for Sigstore's integration into cargo/crates.io.

At the moment, there are two primary OIDC claims from GitHub Actions-issued tokens that get embedded in Fulcio-issued certificates as X.509v3 extensions:

1. The SAN itself, which contains the value of job_workflow_ref from the OIDC token
2. 1.3.6.1.4.1.57264.1.5, which contains the value of the repository claim from the OIDC token (in org/repo "slug" form)

These are sufficient for verification at a point in time, but some threat models may require the assertion that org/repo still refers to the same org and repo. Fortunately, GitHub provides stable numeric identifiers for these, in the form of the repository_id and repository_owner_id claims. These can be used to detect a change in underlying account or repository identity, e.g. in the case an attacker takes over a deleted GitHub account and attempts to release malicious updates with otherwise valid-looking claims.

So, my actual suggestion: we could add two new X.509v3 extensions (and corresponding OIDs):

• 1.3.6.1.4.1.57264.1.8: GitHub Workflow Repository ID: the stable numeric identifier for the repository the workflow was run under
• 1.3.6.1.4.1.57264.1.9: GitHub Workflow Repository Owner ID: the stable numeric identifier for the user or organization that owns the repository the workflow was run under

cc @asraa, @znewman01, and @haydentherapper for thoughts!