A bit of an old post, but I can fill in some info on the link since I am getting feedback that some users are having issues with this.
WHen you have the permanent onguard agent installed, and there is a updated version on the clearpass server, you get a notification popoup.
That notification window have a link to click for installing the updated version, and this one is https.
I have yet to verify if the behavior is constant or not myself.