Is it possible to set up a different external usermin port?

Hi there,

I have a little problem with Usermin and trouble finding anything useful as the keywords bring up "normal" problems regarding port configuration.

In my case I have a Nginx SSL proxy server which handles all external requests. For me it makes a lot of sense because I have a single easy to maintain place for my certificates. Now I also want to make Usermin reachable for external users through this SSL proxy under the subdomain https://usermin.example.com

Nginx is configured correctly with valid certificates and proxy_pass https://10.0.12.70:20000; where 10.0.12.70 is the internal IP of my Usermin server. Obviously Usermin is also running fine and working well when accessed from within the intranet via https://10.0.12.70:20000.

The problem now is when I access it via https://usermin.example.com I get the login mask and everything correctly, however, up on login Usermin redirects to https://usermin.example.com:20000 which fails and makes it unusable as the external port is not 20000 but the SSL proxys default port 443. With normal apps those problems don't occur as the actual external domain is either configurable or obtained dynamically via request headers or not required for link building at all. The question now is, is there an easy way to configure Usermin in this matter, too or do I have to fiddle with its CGIs or mangle outgoing packages? If there is no easy option, what would be the best available way or workaround (and unfortunately in the current setup setting the actual Usermin port simply to 443 too is not so easy for me as it would mean I'd have to move it to another server where this port is available)?

Thanks for any tips!