Question

I am using the Authorize attribute like this:

[Authorize (Roles="Admin, User")]
Public ActionResult Index(int id)
{
    // blah
}

When a user is not in the specified roles, I get an error page (resource not found). So I put the HandleError attribute in also.

[Authorize (Roles="Admin, User"), HandleError]
Public ActionResult Index(int id)
{
    // blah
}

Now it goes to the Login page, if the user is not in the specified roles.

How do I get it to go to an Unauthorized page instead of the login page, when a user does not meet one of the required roles? And if a different error occurs, how do I distinguish that error from an Unauthorized error and handle it differently?

Answer 1

Add something like this to your web.config:

<customErrors mode="On" defaultRedirect="~/Login">
     <error statusCode="401" redirect="~/Unauthorized" />
     <error statusCode="404" redirect="~/PageNotFound" />
</customErrors>

You should obviously create the /PageNotFound and /Unauthorized routes, actions and views.

EDIT: I’m sorry, I apparently didn’t understand the problem thoroughly.

The problem is that when the AuthorizeAttribute filter is executed, it decides that the user does not fit the requirements (he/she may be logged in, but is not in a correct role). It therefore sets the response status code to 401. This is intercepted by the FormsAuthentication module which will then perform the redirect.

I see two alternatives:

1. Disable the defaultRedirect.

2. Create your own IAuthorizationFilter. Derive from AuthorizeAttribute and override HandleUnauthorizedRequest. In this method, if the user is authenticated do a redirect to /Unauthorized

I don’t like either: the defaultRedirect functionality is nice and not something you want to implement yourself. The second approach results in the user being served a visually correct “You are not authorized”-page, but the HTTP status codes will not be the desired 401.

I don’t know enough about HttpModules to say whether this can be circumvented with a a tolerable hack.

EDIT 2:
How about implementing your own IAuthorizationFilter in the following way: download the MVC2 code from CodePlex and “borrow” the code for AuthorizeAttribute. Change the OnAuthorization method to look like

    public virtual void OnAuthorization(AuthorizationContext filterContext)
    {
        if (AuthorizeCore(filterContext.HttpContext))
        { 
            HttpCachePolicyBase cachePolicy = filterContext.HttpContext.Response.Cache;
            cachePolicy.SetProxyMaxAge(new TimeSpan(0));
            cachePolicy.AddValidationCallback(CacheValidateHandler, null /* data */);
        }
        // Is user logged in?
        else if(filterContext.HttpContext.User.Identity.IsAuthenticated)
        {
            // Redirect to custom Unauthorized page
            filterContext.Result = new RedirectResult(unauthorizedUrl);
        } 
        else {
            // Handle in the usual way
            HandleUnauthorizedRequest(filterContext);
        }
    }

where unauthorizedUrl is either a property on the filter or read from Web.config.

You could also inherit from AuthorizeAttribute and override OnAuthorization, but you would end up writing a couple of private methods which are already in AuthorizeAttribute.