@Nullable
    private static List<String> extractSignedHeaders(String authorization) {
        int index = authorization.indexOf("SignedHeaders=");
        if (index < 0) {
            return null;
        }
        int endSigned = authorization.indexOf(',', index);
        if (endSigned < 0) {
            return null;
        }
        int startHeaders = authorization.indexOf('=', index);
        return Splitter.on(';').splitToList(authorization.substring(
                startHeaders + 1, endSigned));
    }
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