OmniAuth callback controller with twitter handler

omniauth_callbacks_controller.rb

#app/controllers/users/omniauth_callbacks_controller.rb
class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController  
  def twitter
    # You need to implement the method below in your model
    auth = env["omniauth.auth"]
    @user = user = User.find_by_provider_and_uid(auth["provider"], auth["uid"]) || User.new
    if @user.persisted?
      flash[:notice] = I18n.t "devise.omniauth_callbacks.success"
      sign_in_and_redirect @user, :event => :authentication
    else
      session["devise.twitter_uid"] = auth["uid"]
      redirect_to new_user_registration_url
    end
  end
end