Additional fix for oauth proxy regression 

Additional fix for oauth proxy regression introduced in edcb7a8  which does not propagate the HTTP proxy config to OAuth anymore. Sorry I initially missed this one.

Propagating fix to refreshToken() which was also impacted. Moved the propagation of the request factory into the createResourceOwnerPasswordAccessTokenProvider() method.  It was hard/verbose to unit test this with little added value. I'll rather complete the integration test which is still on my todo list.