[Evolution] CalDAV is readonly

[Krauß, Peter (SCC) <peter krauss kit edu>]

Hello everyone,

I tried to conenct my work calendar (provided by some Exchange server)
via CalDAV to Evolution.

However it is considered /readonly/ for some reason. How can I make it
writeable? I started the calendar factory in debug mode (CALDAV_DEBUG=all and -w flag) to see what the server 
provides:

...
Allow: OPTIONS, PROPFIND, HEAD, GET, REPORT, PROPPATCH, PUT, DELETE,
POST          <-- I guess the HTML actions are fine...
...

The reply to the PROPFIND request is this:  

...
<?xml version="1.0" encoding="UTF-8" ?>
<D:multistatus xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav"
xmlns:E="urn:ietf:params:xml:ns:carddav">
    <D:response>
        <D:href>/users/peter krauss kit edu/calendar/</D:href>
        <D:propstat>
            <D:prop>
                <D:current-user-privilege-set>
                    <D:privilege>
                        <D:read />
                        <D:write />  <-- I guess this means I can write
                    </D:privilege>
                </D:current-user-privilege-set>
            </D:prop>
            <D:status>HTTP/1.1 200 OK</D:status>
        </D:propstat>
    </D:response>
</D:multistatus>
...


Is there something I do wrong? Maybe a way to override those settings?

Thanks in advance,
Peter