Something like this would work (now, mind you this isn’t HTTPS, if you REQUIRE this I can probably whip something up for you)
server {
listen 80;
server_name yoursqueezeboxIP/whatever if necessary;
location / {
proxy_pass http://yourinternaltld.com/app;
#proxy_pass http://www.yourexternaltld.com/app; <-- if you actually are forwarding port 80 to the internet, but I don't recommend this at all.
}
}
Save that as your nginx config and you shouldn’t have to do much more other than fill in the example slots. I would advise running Nginx on a separate VM or dedicated machine.