code: def calls(self):
          
          if self._calls is None:
              self._calls = AuthTypeCallsList(
                  self._version,
                  account_sid=self._solution['account_sid'],
                  domain_sid=self._solution['domain_sid'],
              )
          return self._calls
docs: Access the calls
  
          :returns: twilio.rest.api.v2010.account.sip.domain.auth_types.auth_calls_mapping.AuthTypeCallsList
          :rtype: twilio.rest.api.v2010.account.sip.domain.auth_types.auth_calls_mapping.AuthTypeCallsList