private static byte[] signMessage(byte[] data, byte[] key, String algorithm)
            throws InvalidKeyException, NoSuchAlgorithmException {
        Mac mac = Mac.getInstance(algorithm);
        mac.init(new SecretKeySpec(key, algorithm));
        return mac.doFinal(data);
    }
Create Amazon V2 signature.  Reference:
http://docs.aws.amazon.com/general/latest/gr/signature-version-2.html
src/main/java/org/gaul/s3proxy/AwsSignature.java