Fixes errors when token endpoint fails

Checking for parameters existence stops the server from ending when the token endpoint fails.

Not try to parse the token if the token endpoint response was OK.
Incorrect Error Check
Fix client_secret

The kid JOSE header was wrong.
Ended up patching jsonwebtoken to fix it. awlayton/node-jsonwebtoken@b82831b
Fix bad stuff from pull request #1 from abalmos/patch-1