public String getAWSSecretKey() {
        return null;
    }
Basic implementation of the AWSCredentials interface that allows use of "anonymous"
credentials.  Using anonymous credentials will result in requests not being signed
before sending to the service.  Any service that does not accept unsigned requests
will return a service exception in this case.
aws-java-sdk-core/src/main/java/com/amazonaws/auth/AnonymousAWSCredentials.java