NocoDB: OAuth Authorization Code Race Condition

Summary

Two concurrent token-exchange requests using the same OAuth authorization code could
each mint a distinct valid (access_token, refresh_token) pair, breaking the
single-use guarantee that PKCE relies on.

Details

The token-exchange flow read is_used and called markAsUsed as an unconditional
update at the end of the path. A new OAuthAuthorizationCode.claimByCode method now
performs an atomic compare-and-swap (WHERE code = ? AND is_used = false) and is
called immediately before OAuthToken.insert, after redirect-URI, PKCE, and client
authentication have all succeeded. Only the first concurrent caller's UPDATE wins;
the rest see invalid_grant: Authorization code has already been used.

Impact

An attacker who has observed an authorization code and the corresponding PKCE
verifier (for example through a malicious OAuth-aware client or by racing a real
exchange) could obtain a long-lived refresh token in addition to the legitimate one.

Credit

This issue was reported by @eddieran.