code: public void observePreNavigateEvent(@Observes PreNavigateEvent event) {
          log.debugf("PreNavigateEvent observed %s, %s", event.getOutcome(), event.getFromAction());
          if (Identity.RESPONSE_LOGIN_SUCCESS.equals(event.getOutcome())
                  && "#{identity.login}".equals(event.getFromAction())) {
              FacesContext context = event.getContext();
              Map<String, Object> sessionMap = context.getExternalContext().getSessionMap();
              postLoginEvent.fire(new PostLoginEvent(context, sessionMap));
          }
      }
docs: Monitor PreNavigationEvents, looking for a successful navigation from the Seam Security login button.  When such a
  navigation is encountered, redirect to the the viewId captured before the login redirect was triggered.
  
  @param event