How to Create rack-app extension

my_new_rack_app_extension.rb

Rack::App::Extension.register 'rack_app_extension'  do

  include ExampleExtensionEndpointMethods
  extend ExampleExtensionClassMethods

  def endpoint_method
    'hello world'  
  end 

  apply_extension :front_end
  
  helpers do 
    def some_template_method
    end
  end
  
end