[Bug]: iMip reply from outlook.com does not contain organizer property

[kesselb]

Bug description

An iMip reply from outlook.com (prod id: Microsoft Exchange Server 2010) does not contain an organizer property.

Our understanding of the RFC, https://datatracker.ietf.org/doc/html/rfc5546#section-3.2.3, is that the organizer property should be included/copied from the original event.

We currently enforce at

server/lib/private/Calendar/Manager.php

Lines 362 to 365 in 8210e12

	if (!isset($vEvent->ORGANIZER)) {
	$this->logger->warning('iMip message event dose not contains an organizer');
	return false;
	}

and

server/apps/dav/lib/CalDAV/CalendarImpl.php

Lines 232 to 234 in 8210e12

	if (!isset($vEvent->{'ORGANIZER'}) || !isset($vEvent->{'ATTENDEE'})) {
	throw new CalendarException('Could not process scheduling data, neccessary data missing from ICAL');
	}

and thus iMIP replies from outlook.com are not processed pr

Steps to reproduce

1. Have mail app enabled (to forward incoming iMip messages from mail to server)
2. Create a event in calendar and invitate a outlook.com user
3. As outlook.com user: accept the invitation
4. See the calendar event is updated and the state in oc_mail_messages is imip_message = true, imip_processed = false, imip_error = true

Expected behavior

The invitation should be processed

Nextcloud Server version

master