CalDAV birthday calendar: modifying birthdays should return 403 instead of 404

[rfc2822]

Currently, modifying birthday events in the birthday calendar (the one which is automatically created and filled with contact birthdays by Nextcloud) over CalDAV PUT returns HTTP 404 with this message:

<?xml version="1.0" encoding="utf-8"?>
<d:error xmlns:d="DAV:" xmlns:s="http://sabredav.org/ns">
  <s:exception>Sabre\DAV\Exception\NotFound</s:exception>
  <s:message>Node with name 'contacts-pas-id-565B107600000032.vcf.ics' could not be found</s:message>
</d:error>

(Reference: https://forums.bitfire.at/post/10439)

I think it would be better to return 403 Forbidden on PUT, because the iCalendar resource exists when downloading it. 404 would mean that there is no representation for this resource. With 403, clients and users can see that the resource is available, but cannot be modified.

[nextcloud-bot]

GitMate.io thinks possibly related issues are #8766 (Caldav ), #5077 (Propatch to birthday calendar returns 404), #8529 (NC 13: disable birthday calendar returns 302 with no feedback), #3003 (Disable birthday contacts calendar generation for user), and #10761 ([stable13] Fix call to OC.generateUrl for caldav birthday calendar on/off).

[skjnldsv]

@georgehrke

[devvv4ever]

Short addition: If possible, it would be helpful if the error message could be more precise. Suggestion: "Contact birthdays is read-only. Please edit the contact itself to change this resource".