Use Omniauthable user model with admin role

app/controllers/admin_controller.rb

@@ -1,3 +1,8 @@
 class AdminController < ApplicationController
-  before_action :authenticate_admin!
+  before_action :authenticate!
+
+  def authenticate!
+    authenticate_user!
+    raise SecurityError unless current_user.admin?
+  end
 end

app/controllers/users/omniauth_callbacks_controller.rb

@@ -0,0 +1,14 @@
+class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
+  skip_before_action :verify_authenticity_token
+
+  def sign_in_with(provider_name)
+    @user = User.from_omniauth(request.env["omniauth.auth"])
+    @user.remember_me!
+    sign_in_and_redirect @user, event: :authentication
+    set_flash_message(:notice, :success, kind: provider_name) if is_navigational_format?
+  end
+
+  def developer
+    sign_in_with "Developer"
+  end
+end