function randomString(length = 16) {
  const chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+/';
  const charCount = chars.length;
  let str = '';
  while (length-- > 0) {
    str += chars[Math.floor(Math.random() * charCount)];
  }
  return str;
}