code: def add_webhook(self, scaling_group, policy, name, metadata=None):
          
          uri = "/%s/%s/policies/%s/webhooks" % (self.uri_base,
                  utils.get_id(scaling_group), utils.get_id(policy))
          body = self._create_webhook_body(name, metadata=metadata)
          # "body" needs to be a list
          body = [body]
          resp, resp_body = self.api.method_post(uri, body=body)
          data = resp_body.get("webhooks")[0]
          return AutoScaleWebhook(self, data, policy, scaling_group)
docs: Adds a webhook to the specified policy.