This document discusses HTTP middlewares in PHP. It begins by introducing the concept of middlewares and how they allow code to be run before and after each HTTP request is handled. It then provides examples of how to implement middlewares using the Symfony HttpKernel component, including logging, caching, and authentication middlewares. Finally, it promotes a PHP middleware stack called StackPHP that provides common middlewares like sessions, OAuth, CORS, and more to simplify building middleware-based PHP applications.