fix(oauth-provider): PAR rejects unregistered redirect_uri#184
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runPostCallback was marking every PRE_REDIRECT_STEPS entry as 'pass' regardless of its actual outcome before the redirect — so any failure in the pre-redirect leg (PAR boundary tests, scope selection, metadata validation, etc.) would silently become green once the user came back from the auth server. Snapshot each pre-redirect step (status, message, evidence, timings) into the persisted state alongside codeVerifier/stateNonce, and restore from it after the callback. If no persisted result is present (older session storage), the steps render as 'skip' with a 'no persisted result' message rather than a fabricated pass.
RFC 6749 §3.1.2.4 requires the authorization server to reject any redirect_uri that was not registered in the client metadata. Cirrus checked this at the authorize step (provider.ts:370) but not at PAR, so a caller could obtain a valid request_uri for an unregistered redirect — defense-in-depth weakness flagged by pdscheck's flow.par-rejects-unregistered-redirect-uri check. Wire the existing ClientResolver into PARHandler and validate redirect_uri against client.redirectUris before issuing the request_uri. Adds a regression test covering the rejection.
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Summary
pdscheck's `flow.par-rejects-unregistered-redirect-uri` step caught a defense-in-depth gap: Cirrus's PAR endpoint accepted any `redirect_uri` whose URL parsed cleanly, regardless of whether it was registered in the client metadata. RFC 6749 §3.1.2.4 requires rejection at this point. The subsequent `/oauth/authorize` step does re-validate (`provider.ts:370`), so the practical exploitability was limited — but issuing a `request_uri` for an unregistered redirect is itself a spec violation and a footgun if any code path elsewhere ever trusted the PAR-stored `redirect_uri` without re-checking.
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