Pointing subdomain to different domain with port

Hello.

I can't figure out how to point a subdomain to a certain port on different domain while keeping the original domain in the URL.

In short, how do I make 'confluence.mydomain.com' point to 'user.asuscomm.com:8090', while keeping 'confluence.mydomain.com' in the address field? I can only get it to redirect, so it gets the new address in the address field.

Thanks for any help.

 

Thank you for your reply. I wonder if I might not have access to editing the Apache .conf files. Also, my situation has changed a little. My ISP has set me up with a static IP address to avoid using the DDNS service. So to be correct, I'm creating a new thread instead of modifying the original question in this one.