I have been doing some more investigating and am getting a step closer.
I noticed that it has to do with closing down the firewall. If I enable tcp port 443 in the INPUT chain and then go to use the web interface, I get to the login screen. However, when I login it will tell me “Login failed!!!”. When I have the firewall completely open, I can login.
The question then becomes: with respect to firewall configuration, other than port 443, what other rules are required to make the web interface work?