class ActionController::Metal

def self.middleware

in the guides.
stack}[https://guides.rubyonrails.org/rails_on_rack.html#action-dispatcher-middleware-stack]
Read more about {Rails middleware

end
use AuthenticationMiddleware, except: [:index, :show]
class PostsController < ApplicationController

allows for the following syntax:
By default uses a variation of ActionDispatch::MiddlewareStack which

The middleware stack used by this controller. 
def self.middleware
  middleware_stack
end