private String getUTCTimestamp() {
        SimpleDateFormat sdf = new SimpleDateFormat(YYYY_MM_DD_T_HH_MM_SS_Z);
        sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
        return sdf.format(new Date());
    }

    private String getNonce() {
        byte[] nonceBytes = new byte[16];
        new java.util.Random().nextBytes(nonceBytes);
        return bytesToHex(nonceBytes);
    }