[horde] Authentication Carddav

[pillul]

Hey,

i try to get Carddav runing using a global adressbook.
I added a new adressbook and checked that "authorized users" are allow to  
access it.
My authentication works against an IMAP Server.
If i try to open the carddav adresse (like:  
https://domain.de/mail/rpc.php/addressbooks/user@domain.de/contacts:Rmjw-T3hA3KT-dsaWYmCKA1/  
i get prompted for my login data.
I enter my email and password (the same i use for log in via horde and the  
imap server) but i get an access denied error:

<d:error>
<s:exception>Sabre\DAV\Exception\NotAuthenticated</s:exception>
<s:message>No basic authentication headers were found</s:message>
<s:sabredav-version>1.8.4</s:sabredav-version>
</d:error>

Did i miss something?

Thank You!