docs: public static String HmacSHA512(String value, String secret) {
      String result;
      try {
        Mac hmacSHA512 = Mac.getInstance("HmacSHA512");
        SecretKeySpec secretKeySpec = new SecretKeySpec(secret.getBytes(), "HmacSHA512");
        hmacSHA512.init(secretKeySpec);
  
        byte[] digest = hmacSHA512.doFinal(value.getBytes());
        BigInteger hash = new BigInteger(1, digest);
        result = hash.toString(16);
        if ((result.length() % 2) != 0) {
          result = "0" + result;
        }
      } catch (InvalidKeyException | NoSuchAlgorithmException ex) {
        throw new RuntimeException("Problem as HMAC", ex);
      }
      return result;
    }