code: func String(l int) string {
  	bs := make([]byte, l)
  	for i := range bs {
  		bs[i] = randomCharset[defaultSecureRand.Intn(len(randomCharset))]
  	}
  	return string(bs)
  }
docs: // String returns a strongly random string of characters (taken from
  // randomCharset) of the specified length. The returned string contains ~5.8
  // bits of entropy per character, due to the character set used.