Tim McLean discovered that pyjwt, a Python implementation of JSON Web Token, would try to verify an HMAC signature using an RSA or ECDSA public key as secret. This could allow remote attackers to trick applications expecting tokens signed with asymmetric keys, into accepting arbitrary tokens. For more information see: https://auth0.com/blog/2015/03/31/critical-vulnerabilities-in-json-web-token-libraries/