JSF page does not properly set object attributes

Simple question from a beginner at JSF:

I have very simple JSF form:

<h:form>
 <p>#{messages.loginTextfieldUsername}</p>
 <h:inputText value="#{userServiceImpl.user.name}" />
 
 <p>#{messages.loginTextfieldPassword}</p>
 <h:inputSecret value="#{userServiceImpl.user.password}" />
 
 <h:commandButton value="#{messages.loginButtonLogin}" action="#{userServiceImpl.authenticateUser}" />
 </h:form>
 

The userServiceImpl class is:

@Named
 @RequestScoped
 public class UserServiceImpl implements UserService {
 
 private UserSession userSession;
 private User user;
 
 @Inject
 public UserServiceImpl(UserSession userSession) {
     this.userSession = userSession;
 }
 
 @PostConstruct
 public void prepareService() {
     user = new User();
 }
 
 @Override
 public View authenticateUser() {
     userSession.setLoggedUser(user);
     return View.MAIN;
 }
 
 public User getUser() {
     return user;
 }
 
 public void setUser(User user) {
     this.user = user;
 }
 

}

My goal is pretty simple: when the user hits the login button, I want to authenticate the user.

The problem is:
When the authenticate method is called, the User attributes are null. I debugged the application and the getUser method is called and the values are properly set, but at some point (which I did not find [yet]) before the authenticateUser is called the User attributes are set to null...

I'm aware that this is a pretty basic question... but are you able to point out where my mistake is?

Thanks.

---