MiddlewareStackProxy is a proxy for the Rails middleware stack that allows you to configure middlewares in your application. It works basically as a command recorder, saving each command to be applied after initialization over the default middleware stack, so you can add, swap, or remove any middleware in Rails.
You can add your own middlewares by using the config.middleware.use method:
config.middleware.insert_before Rack::Head, Magical::Unicorns
config.middleware.insert_after Rack::Head, Magical::Unicorns
Middlewares can also be completely swapped out and replaced with others:
config.middleware.swap ActionDispatch::Flash, Magical::Unicorns
And finally they can also be removed from the stack completely: