Oauth2 provider (Doorkeeper?) being an Oauth2 consumer (Devise+OmniAuth) for login

Question

Oauth2 is driving me crazy.

Currently, my Rails application authenticates users through Facebook, and soon other Oauth2 providers, thanks to the beauty of Devise & OmniAuth. User can't sign in with login & password.

But as my application is mainly an API, I also want it to act as an Oauth2 provider, to protect data.

Thus, the user sign in with Facebook -> my application obtain an Access Token, and then -> provides the user a new Access Token to access my API -> my AngularJS application (or any other app) uses this token to access my API without knowing Facebook or Google Access Token. It looks like I need to forward Oauth2 token to client with a custom provider.

I discovered doorkeeper gem... but I can't understand how to articulate it with Devise & Omniauth.

I found many partial answers here, but not a complete one.

I will appreciate any help, good tutorial, or more complete answers.

Answer 1

Here is a simple tutorial to get you started. Thanks to Andrea!
1. Server Application (Devise + Doorkeeper)
http://dev.mikamai.com/post/110722727899/oauth2-on-rails
2. Client Application (Ominauth-oauth2)
http://dev.mikamai.com/post/112508735689/oauth2-on-rails-the-client-application
P.S. Minor Errata!
1. When you generate the APP_ID and SECRET_ID for the client application from the server application - using http://localhost:3000/oauth/applications/new - enter the callback url http://localhost:3001/auth/doorkeeper/callback
Or, if you see this after the error, go back to http://localhost:3000/oauth/applications/ and edit the callback url.
We can't use http://localhost:3001/doorkeeper/callback because this is not the route the tutorial is using from the Client Application.
2. In the client application include the callback action definition as below and change the to_json method to as_json.

../oauth-client/app/controllers/application_controller.rb

class ApplicationController < ActionController::Base
  # Prevent CSRF attacks by raising an exception.
  # For APIs, you may want to use :null_session instead.
  protect_from_forgery with: :exception
  def authentication_callback
    auth = request.env['omniauth.auth']
    render json: auth.as_json
  end

end

Cheers!