Support for HTTP_FORWARDED_PROTO
WHMCS does not currently check the HTTP_FORWARDED_PROTO header to see if the client is using HTTPS,/SSL, and only considers if the server is using hTTPS.
This cuases an issue because WHMCS ignores the URL from the Client request and forwards the client even if the URL from the user's browser matches the SystemURL. In the cases of Proxies, Load Balancers, and SSL termination, WHMCS incorrectly causes an infinite redirect loop.
(As a sidebar, you can add the following code to your configuration.php file as a workaround to make sure WHMCS doesn't redirect incorrectly:
if ($_SERVER['HTTP_X_FORWARDED_PROTO'] == 'https')
The feature request is for WHMCS to support the use of the HTTP_X_FORWARDED_PROTO so that proxies and load balancers with SSL Termination can be used with WHMCS.