Modify passport-oauth2 to accept a different Content-Type

[CakeCrusher]

Currently passport-oauth2 only allows for Content-Type to be application/x-www-form-urlencoded this will allow for the https://www.openplugin.io/ launchpad to be more secure and for a less distributed system architecture.

https://github.com/jaredhanson/passport-oauth2/issues/176