private Callback<Void> routerCallback() {
      return buildCallback(metrics.undeleteBlobRouterMetrics, result -> {
        LOGGER.debug("Undeleted {}", RestUtils.getHeader(restRequest.getArgs(), RestUtils.Headers.BLOB_ID, true));
        restResponseChannel.setHeader(RestUtils.Headers.DATE, new GregorianCalendar().getTime());
        restResponseChannel.setHeader(RestUtils.Headers.CONTENT_LENGTH, 0);
        securityService.processResponse(restRequest, restResponseChannel, null, securityProcessResponseCallback());
      }, restRequest.getUri(), LOGGER, finalCallback);
    }
After {@link Router#undeleteBlob} finishes, call {@link SecurityService#processResponse}.
@return a {@link Callback} to be used with {@link Router#undeleteBlob}.
ambry-frontend/src/main/java/com/github/ambry/frontend/UndeleteHandler.java