Add oAuth2 Authorization Code support

[grispin]

To better support browser based applications to RESO transport interfaces, in-browser authentication should be better supported. The current supported authenticated models focus more on application to application authentication. Bearer token and client credentials are not as browser friendly and require more involvement from the credentials integrator for issuance.

This was orgininally started as an Issue on this project. #27

[SergioDelRioT4Bi]

I think this is a significant benefit to client applications and we should adopt this. Does anyone else have any further comments on this?