Manual Multi-signature JWT verification

[EternalDeiwos]

Current behaviour when calling JWT.verify({ serialized: token, jwk: '...' }) -- where the caller provides the public JWK for signature verification -- is that only one key may be provided.

This problem is only for the case where the caller is passing in the JWKs for signature verification. The default behaviour of using the JWKSet Cache to look up keys etc. will still look up all necessary keys and verify all signatures as expected.