Como usar threads e fazer a página aguardar a requisição ser finalizada. [CompletableFuture<Result> , Firebase]

PlayController.java

/** This method was called by Play! through the some tag in the html */
public CompletableFuture<Result> submit() {
        auth = FirebaseAuth.getInstance(app);
        final Form<LoginForm> filledForm = loginForm.bindFromRequest();
        return signIn(filledForm);
    }

    private CompletableFuture<Result> signIn(Form<LoginForm> filledForm) {
        final CompletableFuture<Result> resultFuture = new CompletableFuture();
        final ApiFuture<UserRecord> firebaseFuture = auth.getUserByEmailAsync(filledForm.get().getEmail());
        ApiFutures.addCallback(firebaseFuture, new ApiFutureCallback<UserRecord>() {
            @Override
            public void onFailure(Throwable throwable) {
                Logger.debug("Erro: " + throwable.getMessage());
                resultFuture.complete(badRequest(views.html.index.render()));
            }

            @Override
            public void onSuccess(UserRecord userRecord) {
                Logger.debug("Logado com sucesso");
                resultFuture.complete(ok(views.html.profile.render(user)));
            }
        });
        return resultFuture;
    }