How do I change the webui's url base for reverse proxy usage?

[Betonhaus]

I'm deploying a docker configuration and want to proxy qbittorrent that's at :8080 to /qbittorrent.
for it to work i need to set qbittorrent to use /qbittorrent/ as the url base, but I can't find the setting in the ui and I don't know the name of the enviroment variable to use