HTTPS conversion tool
From MoodleDocs
The HTTPS conversion tool will convert any embedded HTTP content (not links) on your site to HTTPS in order for it to display correctly on your HTTPS site.
Before performing the conversion, content will be scanned to find any URLs which may not work after conversion i.e. any domains which do not appear to support HTTPS content. After switching to HTTPS, the content included from these sites will no longer display within Moodle for users with secure modern browsers. These problematic domains will be converted, but obviously won't work once the conversion is complete, hence they are reported for audit prior to the conversion process.
