README
https://github.com/mkdynamic/omniauth-facebook
https://github.com/zquestz/omniauth-google-oauth2
Create Google+ application:
https://developers.google.com/+/web/signin/javascript-flow
Create Facebook application:
https://developers.facebook.com/docs/facebook-login/v2.1
https://developers.facebook.com/docs/reference/dialogs/oauth