This is a copy of a question I posted at the Joomla support forums: https://forum.joomla.org/viewtopic.php?f=717&t=957766
When I try to set the Force HTTPS option using the admin facility I get the following warning message:
But if I edit the configuration.php file and set $force_ssl to '2' then it works.
I'm guessing this has something to do with running under IIS and/or running on an Azure VM.
Any suggestions as to how to avoid this problem, or diagnose it further?