code: def _authenticate(self):
          
          login_info = self._apicall('login')
          self.api_session_id = login_info['apisessionid']
          if not self.api_session_id:
              raise Exception('Login failed')
          # query ttl and verify access to self.domain:
          zone_info = self._apicall('infoDnsZone', domainname=self.domain)
          self.zone_ttl = zone_info['ttl']
docs: Authenticate with netcup server. Must be called first.