Enhancement: oauth2 support for stack-oauth

 * quick and dirty 'hack'
 * thoughts?
Don't worry about it just yet. We can circle back to it if needed. :)

If it were for anything other than `HttpFoundation` I might not care. :) For consistency, I think it would be better for `Request` to be used everywhere rather than `HttpFoundation\Request` to be used in just a handful of places. :)