If your site has even one or two actions where access is restricted to particular users, the smart thing to do is to restrict access to all the actions on your site and then selectively permit access to those actions that all users are allowed to request. That way, an error of omission (forgetting to make a method available) simply prevents users from accessing some action.

Unfortunately, by default ASP.NET MVC works exactly the opposite way: all actions are accessible to all users unless you specifically restrict access by applying the Authorization action filter to the method. Under this scenario, an error of omission (forgetting to put an Authorize attribute on a method) allows all users access to the action. It's literally the worst thing that can happen in a secure environment: unauthenticated and unauthorized access to a resource that should have been secured.

Global Filters provided a solution to this by allowing you to apply the Authorize attribute to all of your action methods, locking non-authenticated users out of your actions by default. You can then selectively override that setting by applying the Authorize attribute to individual methods, specifying specific roles and users authorized to use that action. That works, unless you have some action methods that don't require authentication, methods intended to be accessible to the general public. In that scenario, you can't use Global Filters to secure all of your action methods -- until ASP.NET MVC 4.

Implementing the best practice is possible in ASP.NET MVC 4 with the new AllowAnonymous action filter. The first step is to use the Global Filters in the FilterConfig class in the App_Start folder to apply the Authorize attribute to every action method:

public class FilterConfig
{
  public static void RegisterGlobalFilters(GlobalFilterCollection filters)
  {
    filters.Add(new AuthorizeAttribute);
  }
}


The next step is to selectively allow access to actions that don't require authentication by decorating them with the AllowAnonymous attribute:

[AllowAnonymous]
Public ActionResult Get()
{