Fancy web interfaces are road to hell. Do simplest thing that works. Plain apache or nginx with webdav, basic auth(proven code, minimal attack surface). Maybe firewall with ip_hashlimit on new connections. I have it set to 2/minute and for browser it's actually fine, while moronic bots make new connection for every request. When they improve, there's always fail2ban.

That the nas server incl. hostname is public does not bother me then.