code: function codeConfig(config) {
    const conf = Object.create(null);
    for (const key in config.custom) {
      conf[key] = config.custom[key];
    }
    for (const key of ['host', 'port', 'backendPort']) {
      conf[key] = config[key];
    }
    return conf;
  }
docs: Returns only whitelisted and custom config options