Authenticate user by twitter with devise and omniauth

We can authenticate an user with twitter.

Set route as below. This activates callback url from twitter.

  devise_for :users, :controllers => { :omniauth_callbacks => "users/omniauth_callbacks" }
  devise_scope :user do
    get 'sign_in', :to => 'devise/sessions#new', :as => :new_user_session
    get 'sign_out', :to => 'devise/sessions#destroy', :as => :destroy_user_session
  end

Then we need to implement registration sequence.

class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
  def twitter
    @user = User.from_omniauth(request.env["omniauth.auth"])

    if @user.persisted?
      sign_in_and_redirect @user, event: :authentication
      set_flash_message(:notice, :success, kind: "Twitter") if is_navigational_format?
    else
      @user.save!
      redirect_to root_path
    end
  end

  def failure
    redirect_to root_path
  end
end