Once you are authenticated it doesn't matter that you enter different information your session has been authenticated and thus it does not try to do it again.
If you want to authenticate using different credentials then you must make sure you use the appropriate logout method.
I think it is identity.logout();
Think if it just how Windows does not ask you to enter your username and password every time you try to open an application. Once you have logged in then you don't need to do so again until you log out.