Username and password is all you need aside from that.

The sad reality is that Jellyfin’s authentication system is insecure, and there are “anyone can view your content without a valid login” exploits that are not going to be patched. The only way to stop someone would be to include a secondary username+password on your reverse proxy, to prevent attackers from even reaching your Jellyfin login page. Because if you can reach Jellyfin’s login page, you can exploit it without logging in. But that would break basically everything except for web browsers, because none of the various apps have support for more than Jellyfin’s authentication.