Authorization bypass via unchecked HS256 signatures

Improper JWS signature verification in OCaml-JOSE before 0.8.2 allows remote attackers to bypass authorization with forged HS256 tokens. In Jose.Jws.validate, the HS256 path hashes the supplied signature and compares it with a plain SHA-256 digest of the signing input instead of comparing the signature with a keyed HMAC over that input. A reachable service is exposed when it relies on JWS claims without additional checks, allowing altered header or payload claims to cross its authorization boundary.