[MM-18871] Update session in app instance in app layer (#12540)

app/login.go

@@ -162,6 +162,7 @@ func (a *App) DoLogin(w http.ResponseWriter, r *http.Request, user *model.User,
 	}
 
 	w.Header().Set(model.HEADER_TOKEN, session.Token)
+	a.Session = *session
 
 	if pluginsEnvironment := a.GetPluginsEnvironment(); pluginsEnvironment != nil {
 		a.Srv.Go(func() {