@GET
      @Path("test")
      @Produces("text/plain")
      public CompletionStage<String> text(@Context HttpRequest req) {
         System.out.println("application (inline): " + ResteasyProviderFactory.getContextData(Application.class));
         CompletableFuture<String> cs = new CompletableFuture<>();
         ExecutorService executor = Executors.newSingleThreadExecutor();
         executor.submit(
               new Runnable() {
                  public void run() {
                     System.out.println("application (async): " + ResteasyProviderFactory.getContextData(Application.class));
                     cs.complete("hello");
                  }
               });
         return cs;
      }

application (inline): org.jboss.resteasy.experiment.undertow.TestCompletionStage$TestApp@72d370fa
application (async): null