code: def endpoint(self):
          
          if self.endpoint_ref and self.tunnel_interface_ref:
              return InternalEndpoint(href=self.endpoint_ref)
          return Element.from_href(self.endpoint_ref)
docs: Endpoint is used to specify which interface is enabled for
          VPN. This is the InternalEndpoint property of the
          InternalGateway.
          
          :return: internal endpoint where VPN is enabled
          :rtype: InternalEndpoint,ExternalGateway