title: Validate acess token of Facebook + Twitter + Instagram
body: <p>In my app a user can login or register with Facebook, Twitter or Instagram. Fetching and validating access token are done in application (Android and iOS). Now when they send a request for registration, I need to validate the access tokens. Do I have to validate each access token manually like:</p>
  
  <pre><code>facebook_data = HTTParty.get("https://graph.facebook.com/me", query: {
    access_token: params[:access_token]
  }).parsed_response
  
  # You need to implement the method below in your model (e.g. app/models/user.rb)
  @user = User.find_for_facebook_oauth(facebook_data)
  </code></pre>