@ahaw021, the state "closed" commonly means that there is no TCP listener bound to that point, distinct from "filtered" which refers to a firewall preventing connections:
The state is either open, filtered, closed, or unfiltered. Open. means that an application on the target machine is listening for connections/packets on that port. Filtered. means that a firewall, filter, or other network obstacle is blocking the port so that Nmap cannot tell whether it is open or closed. Closed. ports have no application listening on them, though they could open up at any time. Ports are classified as unfiltered. when they are responsive to Nmap's probes, but Nmap cannot determine whether they are open or closed.
@Camaalot, for webroot authentication, you must have an existing web server listening on port 80 that is already reachable from the public Internet. Is that the case in your setup? The evidence from @ahaw021's experiment suggests that you don't have an existing reachable web server, even though I'm not convinced that's necessary due to firewall settings.