If you want FRP, why not just install FRP? It even has a LuCI app to control it from what it looks like.

OpenWRT page showing the availability of FRP as an app

NGINX is also available at a mere 1kb in size for the slim version, full version also available as well as HAproxy. Those will have you more than covered, and support SSL.

Looks like there’s also acme.sh support, with a matching LuCI app that can handle your SSL certificate situation as well.