Add convenience methods to mock Bearer Authentication
Bearer authentication is quite common (OAuth) so it would be nice if MockNetworkAccessManager would have some convenience methods to work with it.
For example, in OAuth 2, an unauthorized request must be responded with an auth challenge as specified in RFC 6750 section 3.
Additionally, when using unsupported authentication schemes, the MockNetworkAccessManager issues two warnings which should be avoided.
Edited by Jochen Ulrich