title: The type or namespace name 'IAuthenticationFilter' could not be found (are you missing a using directive or an assembly reference?)
body: <p>I have a class library and I have added the reference to <strong>System.Web.Mvc</strong> v4.00 but for some reason the <strong>Filters</strong> namespace is unavailable. 
  I am trying to create a custom controller and I have used <strong>ILSpy</strong> to look at the existing class. It has a reference to <strong>System.Web.Mvc.Filters</strong> which I can see when I inspect the assembly but in my project there appears to be no <strong>Filters</strong> namespace.</p>
  
  <p>Does anyone have any idea why?</p>
  
  <p>Cheers.</p>