CVE-2026-102269: PyJWT: Non-canonical signature segments enable raw-token revocation bypass

PyJWT 2.13.0 accepts compact JWS signature segments containing characters that are not in the Base64URL alphabet. Appending !!!! to a valid signature does not change the decoded signature bytes or authenticated claims, but it changes the serialized token and its SHA-256 hash. An application that indexes logout or revocation state by the raw token therefore rejects the logged-out token and accepts its no-key alternate serialization.

This report separates two issues: permissive compact-JWS decoding is the library behavior, while using raw serialized JWT text as a security identity is a dangerous application composition. A jti-indexed control blocks both representations.