UPSTREAM: Support PUT returning 201 on Create
UPSTREAM: Allow Clients to specify a transport on create
Add dependency on RangelReale/osin for OAuth2
Add dependency on RangelReale/osincli for OAuth2
Add dependency on gorilla/sessions and gorilla/securecookie
User and UserIdentityMapping objects

Allows consumers to get or create a mapping between an identity
and a user.
Add an OAuth2 server and authn abstractions