private void start() {
      try {
        RestRequestMetrics requestMetrics =
            frontendMetrics.listBlobsMetricsGroup.getRestRequestMetrics(restRequest.isSslUsed(), false);
        restRequest.getMetricsTracker().injectMetrics(requestMetrics);
        accountAndContainerInjector.injectAccountContainerForNamedBlob(restRequest,
            frontendMetrics.listBlobsMetricsGroup);
        if (namedBlobDb == null) {
          throw new RestServiceException("Named blob support not enabled", RestServiceErrorCode.BadRequest);
        }
        // Start the callback chain by performing request security processing.
        securityService.processRequest(restRequest, securityProcessRequestCallback());
      } catch (Exception e) {
        finalCallback.onCompletion(null, e);
      }
    }
Start the chain by calling {@link SecurityService#preProcessRequest}.
ambry-frontend/src/main/java/com/github/ambry/frontend/NamedBlobListHandler.java