Here we go..
Now, my routers asks me for the external IP address, that bit's easy. It also asks me for the port number to forward FROM. This I don't know. I do know the IP address and port that I am forwarding TO (192.168.0.102:80)
Maybe someone with more knowledge can help but in the past I've had issues accessing the external ip address when connected on the local network but thing that was a router issue.
This is probably not the best solution since there are quite a number of sub-directories in the mongoose tree and it would be a bit of a pain to secure them all using this method.
A better method might be to create the .htpasswd file in /mod/etc then edit /mod/etc/mongoose.conf to include the line:
You may have to restart mongoose after making these changes. It will then ignore any per-directory .htpasswd files and only use /mod/etc/.htpasswd for all directoies.