I'm in the process of moving a number of standalone WP installs into a single multisite and as part of that I'm using the Domain Mapping plugin. I originally setup the primary blog as wpms.screammedia.net and as I'm moving the live domains over, I create a url on the multisite (something like wpms.screammedia.net/newsite) and the later I change the url in the site settings. Then I also map the www version of the site if the original url didn't have the subdomain.
The problem is for some sites that already exist, their SEO is stronger with http://www.domain.com vs domain.com so I try to set the mapping to use the www. It works fine if I don't have https:// as the domain but as soon as I try to use https:// the site continues to redirect to https://domain.com even when the primary domain is https://www.domain.com..
I'm using a VPS with an account in cPanel for the multisite; it has a dedicated IP and I create addon domains for each new installation. I use cPanel's included autoSSL which generates an ssl for each addon domain as well as the mail and www subdomains.