code: func MarshalAuthorizedKey(key PublicKey) []byte {
  	b := &bytes.Buffer{}
  	b.WriteString(key.Type())
  	b.WriteByte(' ')
  	e := base64.NewEncoder(base64.StdEncoding, b)
  	e.Write(key.Marshal())
  	e.Close()
  	b.WriteByte('\n')
  	return b.Bytes()
  }
docs: // MarshalAuthorizedKey serializes key for inclusion in an OpenSSH
  // authorized_keys file. The return value ends with newline.