code: func Sign(message string) string {
  	if len(secretKey) == 0 {
  		return ""
  	}
  	mac := hmac.New(sha1.New, secretKey)
  	if _, err := io.WriteString(mac, message); err != nil {
  		utilLog.Error("WriteString failed", "error", err)
  		return ""
  	}
  	return hex.EncodeToString(mac.Sum(nil))
  }
docs: // Sign a given string with the app-configured secret key.
  // If no secret key is set, returns the empty string.
  // Return the signature in base64 (URLEncoding).