Will be good to see the latest answer from days ago on the following 3 years old topic worth to be added to docs.
I see this is very helpful for many people to be there in the docs, as it really shows that we don't need to install full-fledged http server like nginx to get luci to work with reverse proxy with custom url.
Accessing LUCI over Reverse Proxy - Installing and Using OpenWrt - OpenWrt Forum