EEF-CVE-2026-78223

Token revocation record built from unverified JWT claims in AshAuthentication

## Summary Improper Verification of Cryptographic Signature vulnerability in team-alembic AshAuthentication allows a caller of the token revocation action to neutralise a revocation or write arbitrary rows into the token resource. `AshAuthentication.TokenResource.RevokeTokenChange.change/3` reads the `:token` argument and decodes it with `AshAuthentication.Jwt.peek/1`, which delegates to `Joken.peek_claims/1` and performs no signature check, unlike `Jwt.verify/4`. The `jti`, `exp` and `sub` claims it returns are written straight onto the revocation record, guarded only by `byte_size(token) > 0`. Because `expires_at` derives from the attacker-chosen `exp`, a forged copy of a genuine token that keeps the real `jti` but backdates `exp` yields a revocation row that is already expired: `expunge_expired` removes it and the genuine token passes `revoked?` again. Arbitrary `jti` and `sub` values can be inserted the same way. This issue affects ash_authentication: from 0.2.0 before 4.15.0 and from 5.0.0-rc.0 before 5.0.0-rc.14.