Question

How can I create a “security aware” action link that detects if a user is authorized to click (invoke) the action?
Hide link if user is not allowed to use that action…

Depending from

• web.config (authorization) and
• [Authorize] attributes on actions

PS
I guess it is bad practice to mix those 2 in MVC?

Answer 1

This is some code poached from the MvcSitemap project and modified for my own use. If I remember correctly this code has been modified for MVC2 and some of the functions might have to be back ported to MVC1.

Its not bad practices at all to mix MVC and FormsAuthentication together, MVC’s default authentication methods are build around the existing Asp.net security infrastructure.

Code to determine if user has permissions:

public static class SecurityTrimmingExtensions 
{

    public static bool HasActionPermission( this HtmlHelper htmlHelper, string actionName, string controllerName )
    {
        //if the controller name is empty the ASP.NET convention is:
        //"we are linking to a different controller
        ControllerBase controllerToLinkTo = string.IsNullOrEmpty(controllerName) 
                                                ? htmlHelper.ViewContext.Controller
                                                : GetControllerByName(htmlHelper, controllerName);

        var controllerContext = new ControllerContext(htmlHelper.ViewContext.RequestContext, controllerToLinkTo);

        var controllerDescriptor = new ReflectedControllerDescriptor(controllerToLinkTo.GetType());

        var actionDescriptor = controllerDescriptor.FindAction(controllerContext, actionName);

        return ActionIsAuthorized(controllerContext, actionDescriptor);
    }


    private static bool ActionIsAuthorized(ControllerContext controllerContext, ActionDescriptor actionDescriptor)
    {
        if (actionDescriptor == null)
            return false; // action does not exist so say yes - should we authorise this?!

        AuthorizationContext authContext = new AuthorizationContext(controllerContext);

        // run each auth filter until on fails
        // performance could be improved by some caching
        foreach (IAuthorizationFilter authFilter in actionDescriptor.GetFilters().AuthorizationFilters)
        {
            authFilter.OnAuthorization(authContext);

            if (authContext.Result != null)
                return false;
        }

        return true;
    }

    private static ControllerBase GetControllerByName(HtmlHelper helper, string controllerName)
    {
        // Instantiate the controller and call Execute
        IControllerFactory factory = ControllerBuilder.Current.GetControllerFactory();

        IController controller = factory.CreateController(helper.ViewContext.RequestContext, controllerName);

        if (controller == null)
        {
            throw new InvalidOperationException(

                String.Format(
                    CultureInfo.CurrentUICulture,
                    "Controller factory {0} controller {1} returned null",
                    factory.GetType(),
                    controllerName));

        }

        return (ControllerBase)controller;
    }

}

Html Helpers

public static class SecurityTrimmedLink
{
    public static MvcHtmlString SecurityTrimmedActionLink(this HtmlHelper htmlHelper, string linkName, string actionName)
    {
        return htmlHelper.HasActionPermission(actionName, "")
                   ? htmlHelper.ActionLink(linkName, actionName)
                   : MvcHtmlString.Create("");
    }        

    public static MvcHtmlString SecurityTrimmedActionLink(this HtmlHelper htmlHelper, string linkName, string actionName, RouteValueDictionary routeValueDictionary )
    {
        return htmlHelper.HasActionPermission(actionName, "")
                   ? htmlHelper.ActionLink(linkName, actionName, routeValueDictionary)
                   : MvcHtmlString.Create("");
    }

    public static MvcHtmlString SecurityTrimmedActionLink(this HtmlHelper htmlHelper, string linkName, string actionName, object routeValues, object htmlAttributes )
    {
        return htmlHelper.HasActionPermission(actionName, "")
                   ? htmlHelper.ActionLink(linkName, actionName, routeValues, htmlAttributes)
                   : MvcHtmlString.Create("");
    }

    public static MvcHtmlString SecurityTrimmedActionLink(this HtmlHelper htmlHelper, string linkName, string actionName, string controllerName)
    {
        return htmlHelper.HasActionPermission(actionName, controllerName)
                   ? htmlHelper.ActionLink(linkName, actionName, controllerName)
                   : MvcHtmlString.Create("");
    }

    public static MvcHtmlString SecurityTrimmedActionLink(this HtmlHelper htmlHelper, string linkName, string actionName, string controllerName, object routeValues, object htmlAttributes)
    {
        return htmlHelper.HasActionPermission(actionName, controllerName)
                   ? htmlHelper.ActionLink(linkName, actionName, controllerName, routeValues, htmlAttributes)
                   : MvcHtmlString.Create("");
    }
}

Warning: This won’t work in MVC 5 because the call to FindAction() never returns an action descriptor

I tried to find the issue and couldn’t and ended up programming a work around. 🙁