serve frontend from rails through protected route

app/controllers/application_controller.rb

@@ -1,7 +1,12 @@
 class ApplicationController < ActionController::API
   include Response
+  include ActionView::Layouts
 
   include ActionController::HttpAuthentication::Basic::ControllerMethods
   http_basic_authenticate_with name: ENV['BASIC_AUTH_USERNAME'],
                                password: ENV['BASIC_AUTH_PASSWORD']
+
+  def frontend_index_html
+    render file: 'protected_public/index.html'
+  end
 end