OpenProject reverse proxy

NethServer Version: 7.9
Module: web server / apache

I am running an OpenProject server on a container in Proxmox.

The server is running, and I can access it via its LAN IP.

I have configured a reverse proxy in the Web Server that forwards requests for the FQDN to the LAN IP. The proxy does work, but OpenProject sends a 422 error. It absolutely needs to have

RequestHeader set "X-Forwarded-Proto" https

set in the reverse proxy.

I cannot set this command in the GUI reverse proxy; I am trying to do it using CLI.

The problem is that I can’t find the reverse proxy .conf file in the filesystem. Can someone point me to the location of reverse proxy .conf files or tell me how to edit the .conf files so that I can set this command?