How to sections for EG

[XVincentX]

We need an HOW TO section that would be example driven, showing the people how can you so most common scenarios with configurations and results.

[XVincentX]

I just had a report from an user that abandoned Express Gateway because of the frustration of not being able to make oAuth2 work.

It's a difficult protocol, but we haven't been doing a great job here. We need to do something asap.

@kevinswiber @altsang