In order to test if a connection is being made using SSL encryption you need to use the HTTPS environment variable. This will either be "on" if the request is made over HTTPS or it will be undefined if it is made over HTTP.
Other methods to test for HTTPS may fail on our server architecture.
This is an example rewrite rule that will redirect all requests made over HTTP to the HTTPS URL:
RewriteEngine On
RewriteCond %{ENV:HTTPS} !=on
RewriteRule (.*)
https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]
