A share login setup for two devise models.

dual-login-devise.rb

Rails.application.routes.draw do
  constraints subdomain: "admin" do
  devise_for :admins, skip: [:sessions]
  	devise_scope :admin do
  	  get '/login' => 'admins/sessions#new', as: :new_admin_session
	    post '/login' => 'admins/sessions#create', as: :admin_session
	    get '/logout' => 'admins/sessions#destroy', as: :destroy_admin_session

	    unauthenticated do
			  devise_scope :admin do
			    root to: redirect("/login"), :as => "unauthenticated_admin"
			  end
			end

			authenticated do 
				devise_scope :admin do
			    root to: "admins/sessions#new", :as => "authenticated_admin"
			  end
			end
    end
  end

  devise_for :users, skip: [:sessions]
  devise_scope :user do
    get '/login' => 'users/sessions#new', as: :new_user_session
    post '/login' => 'users/sessions#create', as: :user_session
    get '/logout' => 'users/sessions#destroy', as: :destroy_user_session
  end

	authenticated do
  	devise_scope :user do
  		root to: 'application#index', as: 'authenticated_user_root'
	  end
  end

  unauthenticated do
	  devise_scope :user do
	    root to: redirect('/login'), as: "unauthenticated_user"
	  end
	end
end