Seemed to be server problems:with Digest qop=auth-int, with CalDAV requests in general.
Please keep us up to date about your experience with newer versions of kcaldav.
For reference and transparency: We have created this report on Apple Bug Reporter on 6 May 2017 here: https://bugreport.apple.com/web/?problemID=32036351
Valid all-day events without DTEND are rejected by iCloud CalDAV.
Steps to Reproduce:
PUT this event to a calendar:
BEGIN:VCALENDAR VERSION:2.0 PRODID:+//IDN bitfire.at//DAVdroid/1.5.1 ical4android ical4j/2.x BEGIN:VEVENT DTSTAMP:20170506T214225Z UID:2105fb80-c551-4c05-831a-8402949a15f7 DTSTART;VALUE=DATE:20170504 SUMMARY:Test DESCRIPTION:Test STATUS:CONFIRMED TRANSP:TRANSPARENT END:VEVENT END:VCALENDAR
The resource should be accepted. DTEND is an optional property (https://tools.ietf.org/html/rfc5545#section-3.6.1).
The VEVENT is rejected with
<error xmlns='DAV:'><valid-calendar-object-resource xmlns='urn:ietf:params:xml:ns:caldav'/></error>.
If the same event is uploaded with an additional
DTEND;VALUE=DATE:20170505, no error is reported.
iCloud p23-caldav.icloud.com on 6 May 2017 23:50 Europe/Vienna
According to Apple, the bug report has been closed because I did not provide an iCloud Apple ID.