ruby-jwt: Empty-key HMAC bypass; cross-language sibling of CVE-2026-44351

JWT.decodetoken, '', true, algorithm: 'HS256' accepts an attacker-forged token. OpenSSL::HMAC.digest'SHA256', '', payload returns a valid digest under an empty key, and no raise InvalidKeyError if key.empty? precondition exists in the HMAC algorithm. JWT.decodetoken, "", true, algorithm: 'HS256' ...