code: public static String md5Hex(String s) {
      try {
        MessageDigest messageDigest = MessageDigest.getInstance("MD5");
        byte[] md5bytes = messageDigest.digest(s.getBytes("UTF-8"));
        return ByteString.of(md5bytes).hex();
      } catch (NoSuchAlgorithmException e) {
        throw new AssertionError(e);
      } catch (UnsupportedEncodingException e) {
        throw new AssertionError(e);
      }
    }
docs: Returns a 32 character string containing an MD5 hash of {@code s}.