When we login to WHM/cPanel from WHMCS Client Area, the URL shown is using server's hostname instead of client's domain.
Server hostname: host.server.com
Reseller/Client domain: userdomain.com
if userdomain.com login to cPanel via WHMCS, the url shown will be https://host.server.com:2083
It will be better for whitelabeling if it is shown as https://userdomain.com:2083
is only working if entered directly from browser address bar, not from WHMCS-cPanel integration link)