Auth/myth - before filter - redirect login

Hi,
I seem to be getting stuck in an infinite loop trying to redirect to the myth:auth login page.  I have set up a filter, below. 

In my browser if I navigate to http://mydomain/login the login page is shown, as expected.

But if i navigate to http://mydomain/   i get caught in an infinite loop?

I do not have any routes configured for login, or anything remotely like it.

Can anyone point me in the right direction (excuse the pun)?

PHP Code:

public function before(RequestInterface $request) {    
        if(logged_in()!=true && uri_string()!='login') {        
                return redirect('login');
        }
            
    }