iCal has a nasty input control bug. You can't subscribe to a calendar through an https:// url. The "normal" workaround for this bug is first subscribe to http:// calendar (insecure), then manualy edit ~/Library -> Preferences -> com.apple.iCal.sources.plist and replace http:// with https://. But if you want to share the calendar with "normal" Apple users, you can't ask them to edit their config files... it would be against the evolution (of the species) ;-). The solution:
- Publish the calendar on a secure site. The final URL would be: https://www.secure.tld/dav/calendar.ics
- For the communication with subscribers, use non-secure URL, for example: http://www.nonsecure.tld/dav/calendar.ics.
- On the server where non-secure site is hosted, put the following code in httpd.conf (or in an .htaccess file) inside the scope of the non-secure site:
<Location /dav> RedirectMatch (.*)$ https://www.secure.tld$1 </Location>

