@Override
        public HttpResponse authFailed(HttpService delegate, ServiceRequestContext ctx, HttpRequest req,
                                       @Nullable Throwable cause) throws Exception {
            return HttpResponse.of(HttpStatus.UNAUTHORIZED);
        }
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