private Callback<Void> securityPostProcessRequestCallback(BlobInfo blobInfo) {
      return buildCallback(frontendMetrics.putSecurityPostProcessRequestMetrics, securityCheckResult -> {
        RetainingAsyncWritableChannel channel =
            new RetainingAsyncWritableChannel(frontendConfig.maxJsonRequestSizeBytes);
        restRequest.readInto(channel, fetchStitchRequestBodyCallback(channel, blobInfo));
      }, uri, LOGGER, finalCallback);
    }
After {@link SecurityService#postProcessRequest} finishes, return response for the request.
@return a {@link Callback} to be used with {@link SecurityService#postProcessRequest}.
ambry-frontend/src/main/java/com/github/ambry/frontend/s3/S3MultipartCompleteUploadHandler.java