docs: public Response asynFetch(String url, String bucket, String key) throws QiniuException {
          String requesturl = configuration.apiHost(auth.accessKey, bucket) + "/sisyphus/fetch";
          StringMap stringMap = new StringMap().put("url", url).put("bucket", bucket).putNotNull("key", key);
          byte[] bodyByte = Json.encode(stringMap).getBytes(Constants.UTF_8);
          return client.post(requesturl, bodyByte,
                  auth.authorizationV2(requesturl, "POST", bodyByte, "application/json"), Client.JsonMime);
      }