code: func serverKeyId() string {
  	serverConfigFile := osutil.UserServerConfigPath()
  	if _, err := wkfs.Stat(serverConfigFile); err != nil {
  		if os.IsNotExist(err) {
  			return ""
  		}
  		log.Fatalf("Could not stat %v: %v", serverConfigFile, err)
  	}
  	obj, err := jsonconfig.ReadFile(serverConfigFile)
  	if err != nil {
  		return ""
  	}
  	keyID, ok := obj["identity"].(string)
  	if !ok {
  		return ""
  	}
  	return keyID
  }
docs: // serverKeyId returns the public gpg key id ("identity" field)
  // from the user's server config , if any.
  // It returns the empty string otherwise.