Support oAuth2 - FB, Twitter, Google, etc.

[toenuff]

Below wouldn't be too difficult to include https://github.com/SimpleAuthentication/SimpleAuthentication/wiki/NancyFX-Manual-Setup

I'm tempted to dig through the above and see if we can just do it on the powershell side, but why reinvent?

[apetitjean]

I would advice to take the easiest way and see if we can do better later.