function carddav_addressbook_getctag($server)
 {
     $this->write_log('Getting CardDAV-Addressbook ctag');
     $carddav_backend = new carddav_backend($server['url']);
     if ($this->rc->decrypt($server['password']) == '%p') {
         $server['password'] = $this->rcpassword;
     }
     $carddav_backend->set_auth($server['username'], $this->rc->decrypt($server['password']), $server['authtype']);
     return $carddav_backend->get_ctag(false);
 }