@Override
        public HttpResponse authSucceeded(HttpService delegate, ServiceRequestContext ctx, HttpRequest req)
                throws Exception {
            return delegate.serve(ctx, req);
        }
When the first {@link Authorizer} returns a {@link CompletionStage} that fulfills with {@code null},
the second {@link Authorizer} shouldn't be invoked.
core/src/test/java/com/linecorp/armeria/server/auth/AuthorizerTest.java