[Bug]: `calendar-access` missing from `DAV` header on

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• Nextcloud Server is running on 64bit capable CPU, PHP and OS.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

I'm writing a function to check whether a given URL corresponds to a server supporting CALDAV or not. For this, I'm checking the DAV URL as specified in rfc4791#section-5.1:

A server supporting the features described in this document MUST
include "calendar-access" as a field in the DAV response header from
an OPTIONS request on any resource that supports any calendar
properties, reports, method, or privilege. A value of "calendar-
access" in the DAV response header MUST indicate that the server
supports all MUST level requirements specified in this document.

The URL (https://example.com/remote.php/dav) does support calendar access; I can successfully use REPORT to fetch calendar resources and PROPFIND to enumerate calendar resources and collections, so I'm quite sure I have the right URL.

Steps to reproduce

1. Send an OPTIONS http request.

Expected behavior

The DAV header should contain calendar-access.

Installation method

Other Community project

I don't have access to the server installation; I only have a test account which someone is lending me to test NextCloud support. As such, I don't have most of the below details.

Operating system

Other

PHP engine version

Other

Web server

Other

Database engine version

Other

Is this bug present after an update or on a fresh install?

None

Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

No response

List of activated Apps

No response

Nextcloud Signing status

No response

Nextcloud Logs

No response

Additional info

Version from the about screen:

(I'm not entirely sure why, but text selection for copy-pasting was not possible).

Start by reproducing an OPTIONS request against the mentioned remote.php/dav entry point and inspect how its DAV response header is assembled. Compare the response with the RFC requirement and the existing calendar REPORT and PROPFIND behavior; done means the header includes calendar-access for a resource supporting calendar access.