private URI createEndpoint(String regionName, String serviceName) {
        final Region region = RegionUtils.getRegion(regionName);

        if (region == null) {
            throw new AmazonClientException("{" + serviceName + ", " + regionName + "} was not "
                    + "found in region metadata. Update to latest version of SDK and try again.");
        }

        return toURI(region.getServiceEndpoint(serviceName));
    }
Abstract pre-sign handler that follows the pre-signing scheme outlined in the 'RDS Presigned URL for Cross-Region Copying' SEP.

@param <T> The request type.
aws-java-sdk-neptune/src/main/java/com/amazonaws/services/neptune/PresignRequestHandler.java