Prevent FormsAuthenticationModule of intercepting ASP.NET Web API responses

Question

In ASP.NET the FormsAuthenticationModule intercepts any HTTP 401, and returns an HTTP 302 redirection to the login page. This is a pain for AJAX, since you ask for json and

Answer 1

In case someone's interested in dealing with the same issue in ASP.NET MVC app using the Authorize attribute:

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, Inherited = true, AllowMultiple = true)]
public class Authorize2Attribute : AuthorizeAttribute
{
    protected override void HandleUnauthorizedRequest(AuthorizationContext filterContext)
    {
        if (filterContext.HttpContext.Request.IsAuthenticated)
        {
            filterContext.Result = new HttpStatusCodeResult((int) HttpStatusCode.Forbidden);
        }
        else
        {
            if (filterContext.HttpContext.Request.IsAjaxRequest())
            {
                filterContext.HttpContext.Response.SuppressFormsAuthenticationRedirect = true;
            }
            base.HandleUnauthorizedRequest(filterContext);
        }
    }
} 

This way browser properly distinguishes between Forbidden and Unauthorized requests..