Added basic OAuth2 backend for Microsoft Azure Active Direcotory (Ofice365).

[shaib]

Hi,

This adds a basic backend for authentication with Microsoft Azure's Active Directory service, which is itself the engine behind Office365 authentication.

(would it be ok to add a reference to https://github.com/SlateScience/ to the "thanks" file?)

Thanks,
Shai, for SlateScience.

[omab]

Is this related to #632 on any way?

[shaib]

Yes, in fact, #632 is a fuller implementation of the same thing. This is no longer required (I took time to verify that the now-built-in implementation works for us before confirming).