How is this expected to work for apps that having a webserver fronting the app that terminates TLS/QUIC/HTTP3 and proxies over fastcgi/http1.1/h2c for example?

How is this expected to work for apps that having a webserver fronting the app that terminates TLS/QUIC/HTTP3 and proxies over fastcgi/http1.1/h2c for example? Specifically, how would this work for say, a PHP app that wants to stream stuff? I use https://reactphp.org/ https://reactphp.org/ for websockets in PHP (so I can have a shared codebase with my main app, etc). I don't think I understand how this would look on the server-side. I'm interested to understand how it would look like to support this in Caddy (I'm one of the core contributors).