[Ur] Looking for an example of a common pattern

[David Snider]

There is a common pattern in web development of redirecting a user to a 
login page when their login cookie can not be found. If the login is 
invalid it regenerates the page with an error message, otherwise it 
generates the requested page. Could someone show me an example of how to 
use a functor to generate this functionality for any page? I tried this 
myself and ran into issues like having the Login and HomePage module be 
mutually dependent on each other. I am not sure what the correct way to 
do this is.

Thanks