@Override
    public Optional<RequestSigner> getSigner(Class<? extends RequestSigner> requestSignerType) {
        return Optional.ofNullable(signerForType.get(requestSignerType));
    }
Register an requestSigner
@param requestSigner
     an instance of an RequestSigner to use for a given type
@param signerType
     the type of requestSigner that this instance will be used for
aws-java-sdk-opensdk/src/main/java/com/amazonaws/opensdk/protect/auth/RequestSignerRegistry.java