def install_middleware(where, builder)
      verify_middleware_location(where)
      (middleware_installers[where] || []).each do |installer|
        installer.call(builder)
      end
    end
def install_middleware(where, builder)
      verify_middleware_location(where)
      (middleware_installers[where] || []).each do |installer|
        installer.call(builder)
      end
    end
Installs the middleware configured under the given key in the
 given `Rack::Builder}. This method is primarily for internal
 library use.

 @see #register_middleware_installer
 @param [:before_authentication,:after_authentication] where the
   set of middleware installers to use.
 @param [#use] builder the `Rack::Builder`-like object into which
   the middleware will be installed.
 @return [void]