Right click in the calendar list> Add Calendar> iCal Calendar file paste the url (looking like https://server/jsp/custom/modules/plannings/direct_cal.jsp?data=4011850addbbf02) in the Filename entry (should be allowed: "A URL of a remote file can also be specified") Check "Read only" OK The dialog closes, but no calendar appears. The url is valid, since after a direct download with curl https://server/jsp/custom/modules/plannings/direct_cal.jsp?data=4011850addbbf02 > remotecal.ics and giving the path to remotecal.ics, the calendar appears correctly. The reason why has possibly been given by Markus: https://bugs.kde.org/show_bug.cgi?id=308129#c2
the url no longer exists. can you provide another url for testing purposes?