RouteConstraint to ensure a parameter is a Guid

GuidRouteConstraint.cs

private class GuidRouteConstraint : IRouteConstraint
{
    public bool Match(HttpContextBase httpContext, Route route, string parameterName, RouteValueDictionary values, RouteDirection routeDirection)
    {
        object value;
        if (!values.TryGetValue(parameterName, out value))
        {
            return false;
        }

        object defaultValue;
        if (route.Defaults.TryGetValue(parameterName, out defaultValue) && (value == defaultValue))
        {
            return true;
        }

        Guid guid;
        return Guid.TryParse(value.ToString(), out guid);
    }
}