dashboard-demo - bad login credentials redirect

Hi everybody, 

So I'm pretty new in Vaadin - still learning. And I'm trying to make something like simple login. I saw example of dashboard on git lets focus on this class: 

https://github.com/vaadin/dashboard-demo/blob/master/src/main/java/com/vaadin/demo/dashboard/DashboardUI.java

Method: userLoginRequested .Question is very simple how to show on LoginView some information if user use wrong username / password in loggin proces. As I undestand this login is based on events, problem is that LoginView - https://github.com/vaadin/dashboard-demo/blob/master/src/main/java/com/vaadin/demo/dashboard/view/LoginView.java line 82. Isn't waiting for any response. Is it possible in vaadin to get some response from event ? How can I do this (lets start with simple true / false - this will be enough)