Provide express, payload and done params to secret function

[akaNightmare]

Hi All,
I would be great to provide some params(see subj) to secret functions like https://github.com/auth0/socketio-jwt#getting-the-secret-dynamically

[aembke]

That sounds like a good idea, but since it would require a breaking change to the interface I'm going to hold off on implementing it until the next major release. This module has lagged behind Node/V8 quite a bit and I'd like to rewrite it with ES6, etc.