CVE-2021-44878: Improper Verification of Cryptographic Signature

Pac4j v5.1 allows (by default) clients to accept and successfully validate ID Tokens with none algorithm (i.e., tokens with no signature) which is not secure and violates the OpenID Core Specification. The none algorithm does not require any signature verification when validating the ID tokens, which allows the attacker to bypass the token validation by injecting a malformed ID token using none as the value of alg key in the header with an empty signature value.