Grape API: cannot define helper method in parent api

I'm using Grape API for my application. Firstly, I define a parent api for all other apis to use:

module FrontEnd
  class FrontEndApi < Grape::API
      def authenticated?
       # some code here
      end
  end
end

Secondly, here is my sample api:

module FrontEnd
  module V1
    module Product
      class GetAllProduct < FrontEndApi
        resource :products do
          get do
            authenticated?

          end
      end
  end
end

But when running, I meet exception at line authenticated? with exception is:

NoMethodError (undefined method `authenticated?' for #<#<Class:0x007fe41a106ea8>:0x007fe41b5f9b80>):

Please help me figure out why. Thanks