This PR tightens several OAuth validation paths related to PKCE
handling, redirect URI normalization, and refresh-token replay safety.
What it changes:
- switch redirect URI comparison to ASCII-only normalization for
exact-match checks, avoiding Unicode case-folding surprises
- harden PKCE verification by:
- allowing PKCE omission only when no challenge data was stored
- rejecting exchanges with a missing verifier when PKCE was used
- rejecting malformed challenge state where a challenge exists without a
valid method
- comparing derived challenges with constant-time string matching
- make refresh-token invalidation counter updates conditional on the
previously observed counter value, so stale refresh state cannot be
accepted after the grant changes
Why:
These checks close gaps where:
- redirect URI comparisons could rely on broader Unicode normalization
than intended
- malformed or incomplete PKCE state could be treated too permissively
- concurrent or stale refresh-token use could advance the same grant
more than once
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Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>
Co-authored-by: Nicolas <bircni@icloud.com>
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