External / SSO auth providers

[HeyJoel]

#156 details a requirement for an external auth provider. Typically in the past we have handled SSO using the Cofoundry user/auth primitives to provision an account for an externally authenticated user and log them in. #162 is concerned with better documenting this process, this issue is concerned with providing better integration points and looking at the possibility of creating plugins for various providers to make this process simpler.

Another request is #199 who is looking to be able to integrate an OAuth2 provider to enable an api that powers a mobile app or SPA.

Further investigation is required, but if anyone wants to add any information on additional scenarios or preferred providers, please do so below.

[biapar]

Check here if you want some info ( I'm using it and customize ). I think that maybe we can port some parts of code to integrate an OAuth server. https://github.com/mattbrailsford/umbraco-authu