code: def register_middleware(self, middleware, attach_to="request"):
          
          if attach_to == "request":
              if middleware not in self.request_middleware:
                  self.request_middleware.append(middleware)
          if attach_to == "response":
              if middleware not in self.response_middleware:
                  self.response_middleware.appendleft(middleware)
          return middleware
docs: Register an application level middleware that will be attached
          to all the API URLs registered under this application.
  
          This method is internally invoked by the :func:`middleware`
          decorator provided at the app level.
  
          :param middleware: Callback method to be attached to the
              middleware
          :param attach_to: The state at which the middleware needs to be
              invoked in the lifecycle of an *HTTP Request*.
              **request** - Invoke before the request is processed
              **response** - Invoke before the response is returned back
          :return: decorated method