An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type

Question

Here's a constant class I use to invoke some helpers:

public static class SecurityHelpers
{
    public static string AntiforgeryTokenSalt = "tokenFooYouTolkienBladeRunner";         
}

And here's how I invoke it in one of my forms in my MVC3 web application:

@using (Html.BeginForm("Index", "Checkout", FormMethod.Post))
{   
    <input type="hidden" name="amount" value="@Model.PackageCost"/>
    <input type="hidden" name="currency" value="$"/>
    <input type="hidden" name="itemdescription" value="@Model.PackageDescriptor"/>
    <input type="hidden" name="type" value="digital"/>
    @Html.AntiForgeryToken(App.WebUI.Helpers.SecurityHelpers.AntiforgeryTokenSalt)

    <input type="submit" value="Confirmar" class="btn primary frmsubmit" />
}

And in my Controller:

[HttpPost]
[ValidateAntiForgeryToken(Salt = SecurityHelpers.AntiforgeryTokenSalt)]
public ActionResult Index(decimal amount, string currency, string itemDescription, string type)
{
    if (!User.Identity.IsAuthenticated) return RedirectToAction("LogOn", "Account");
}

The error is fired in my Controller, it says:

An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type

Any ideas why this isn't working? The Salt attribute of the ValidateAntiForgeryToken decorator is a string and my constant is also a string, so I'm confused.

Answer 1

A static string is not a constant.

Try changing

public static string AntiforgeryTokenSalt = "tokenFooYouTolkienBladeRunner"; 

to

public const string AntiforgeryTokenSalt = "tokenFooYouTolkienBladeRunner";