@Restricted(NoExternalUse.class)
    public static String getHexOfSHA256DigestOf(byte[] input) throws IOException {
        //get hex string of sha 256 of payload
        byte[] payloadDigest = Util.getSHA256DigestOf(input);
        return (payloadDigest != null) ? Util.toHexString(payloadDigest) : null;
    }
@Test
    public void testGetHexOfSHA256DigestOf() throws IOException {
        byte[] input = new byte[] {12, 34, 16};
        String str = Util.getHexOfSHA256DigestOf(input);
        assertEquals(str, "134fefbd329986726407a5208107ef07c9e33da779f5068bff191733268fe997");
    }