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