How to force drupal 7 to load HTTPS assets? Environment:
apache + ssl + domain access 

Our drupal 7 site uses domain access multiple sub domains
our server is SSL enabled

if I do not set $base_url in settings.php then all of our assets our loaded via HTTP and the user receives a mixed content error

If I DO set $base_url users are redirected to the default subdomain (e.g. foo.blah.com) instead of their current domain (e.g. bar.blah.com)

My question is, how do I force drupal to load all assets via HTTPS?

That way I can uncomment the #base_url
I updated settings.php with: $base_url = 'https://'.$_SERVER['SERVER_NAME'];