protected String signAndBase64Encode(String data, String key,
            SigningAlgorithm algorithm) throws SdkClientException {
        return signAndBase64Encode(data.getBytes(UTF8), key, algorithm);
    }
Computes an RFC 2104-compliant HMAC signature and returns the result as a
Base64 encoded string.
aws-java-sdk-core/src/main/java/com/amazonaws/auth/AbstractAWSSigner.java