Since it doesn't appear to be supported natively, what's the recommended way of implementing global filters on a per-area basis?
You could use a custom IFilterProvider.
Levi
The reason it's not supported natively is because we want to discourage developers from doing it. Areas are not associated with controllers; they're associated with routes. We wanted to discourage developers from trying to apply authorization or other security-sensitive filters to areas since they can be bypassed.
See How can we set authorization for a whole area in ASP.NET MVC? for more information.
来源：https://stackoverflow.com/questions/5700295/area-global-filters-in-mvc-3