facebook will begin to issue app-scoped user IDs

elsif user_auth["provider"].eql?("facebook")
      
      authentication = Authentication.find_by_provider_and_uid(user_auth['provider'], user_auth['uid'])
      
      if authentication
        @user = authentication.user
        @user.notification_token = user_auth["user"]["notification_token"]
        
        sign_in(:user, @user, store: false)

        render :json => {:status => "success", :user => @user.info} and return
      else
        #Facebook will begin to issue app-scoped user IDs when people first log into an instance of your app coded against v2.0 of the API. With app-scoped IDs, the ID for the same user will be different between apps.
        
        @user = User.where(:email => user_auth["user"]["email"].downcase, :is_completed => true).first
        old_authentication = Authentication.find_by_provider_and_user_id(user_auth['provider'], @user.id)
        
        if old_authentication
          old_authentication.update_attributes(:uid => user_auth['uid'])
          
          render :json => {:status => "success", :user => @user.info} and return
        else
          render :json => {:status => "errored", :error_id => 172, :errors => ["Please sign up using Facebook"]} and return
        end    
      end