code: func (c *cmd) uploadPayload(payload []byte) error {
  	kv := c.apiclient.KV()
  	pair := api.KVPair{
  		Key:     path.Join(c.conf.prefix, c.sessionID, rExecFileName),
  		Value:   payload,
  		Session: c.sessionID,
  	}
  	ok, _, err := kv.Acquire(&pair, nil)
  	if err != nil {
  		return err
  	}
  	if !ok {
  		return fmt.Errorf("failed to acquire key %s", pair.Key)
  	}
  	return nil
  }
docs: // uploadPayload is used to upload the request payload