woodruffw commented 2 months ago

Copying from the doc, from @segiddins: this bullet has some inaccuracies in it:

The leaf certificate has SANs, not a subject (the subject is empty, since we only use SANs)
The leaf's SANs should be checked not against the CSR's subject (which is incomplete and unauthenticated), but against the OIDC credential that accompanied the CSR during issuance
AuthenticationServiceIdentifier doesn't get defined anywhere above, so I think this should probably say something like "encodes the appropriate underlying OIDC IdP issuer" since that's what it means 🙂

I'm happy to send patches for these improvements, either to this PR or as follow-ups once this is merged. Just let me know whatever works best!

_Originally posted by @woodruffw in https://github.com/sigstore/architecture-docs/pull/9#discussion_r1729515261_

woodruffw commented 2 months ago

The above is relevant to this section of the client spec:

1. Perform certification path validation ([RFC 5280 §6](https://datatracker.ietf.org/doc/html/rfc5280\#section-6)) of the returned certificate chain with the pre-distributed Fulcio root certificate(s) as a trust anchor.  
2. Extract a `SignedCertificateTimestamp`, which may be embedded as an X.509 extension in the leaf certificate or attached separately in the `SigningCertificate` returned from the Identity Service. Verify this `SignedCertificateTimestamp` as in [RFC 6962 §3.2](https://datatracker.ietf.org/doc/html/rfc6962#section-3.2), using the public key from the Certificate Transparency Log.  
3. Check that the leaf certificate contains the subject from the certificate signing request and encodes the appropriate `AuthenticationServiceIdentifier` in an extension with OID [`1.3.6.1.4.1.57264.1.8`](https://github.com/sigstore/fulcio/blob/main/docs/oid-info.md\#1361415726418--issuer-v2).

woodruffw commented 2 months ago

sigstore / architecture-docs

Client spec: post-issuance leaf check clarifications #14

19 addresses this.