You need to make sure the reverse proxy forwards all the headers to the FileRun server. In other words, your reverse proxy must be fully transparent.

Here is an Nginx configuration example:

proxy_set_header Host $host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header X-Forwarded-Protocol $scheme;
proxy_set_header X-Forwarded-Port $server_port;