Most common callbacks

Callbacks_from_Common_Providers.md

Callbacks:

• Digital Ocean: http://localhost:3000/users/auth/digitalocean/callback
• Facebook: http://localhost:3000/users/auth/facebook/callback
• Amazon: http://localhost:3000/users/auth/amazon/callback
• Twitter: http://localhost:3000/users/auth/twitter/callback
• Google: http://localhost:3000/users/auth/google_oauth2/callback