ASP.NET MVC 3 - Improved JsonValueProviderFactory using Json.Net

ExampleModel.cs

//Example of a model that won't work with the current JsonValueProviderFactory but will work with JsonDotNetValueProviderFactory
public class CmsViewModel
{
    public bool IsVisible { get; set; }
    public string Content { get; set; }
    public DateTime Modified { get; set; }
    public DateTime Created { get; set; }
    //This property will not work with the current JsonValueProviderFactory
    public dynamic UserDefined { get; set; }
}

Global.asax.cs

using System.Linq;
using System.Web.Mvc;
using System.Web.Routing;

namespace JsonDotNetValueProviderFactoryTestHarness
{
    // Note: For instructions on enabling IIS6 or IIS7 classic mode, 
    // visit http://go.microsoft.com/?LinkId=9394801

    public class MvcApplication : System.Web.HttpApplication
    {
        public static void RegisterGlobalFilters(GlobalFilterCollection filters)
        {
            filters.Add(new HandleErrorAttribute());
        }

        public static void RegisterRoutes(RouteCollection routes)
        {
            routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

            routes.MapRoute(
                "Default", // Route name
                "{controller}/{action}/{id}", // URL with parameters
                new { controller = "TestJsonValueProviderFactory", action = "Index", id = UrlParameter.Optional } // Parameter defaults
            );

        }

        protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();

            RegisterGlobalFilters(GlobalFilters.Filters);
            RegisterRoutes(RouteTable.Routes);

            //Remove and JsonValueProviderFactory and add JsonDotNetValueProviderFactory
            ValueProviderFactories.Factories.Remove(ValueProviderFactories.Factories.OfType<JsonValueProviderFactory>().FirstOrDefault());
            ValueProviderFactories.Factories.Add(new JsonDotNetValueProviderFactory());
        }
    }
}

JsonDotNetValueProviderFactory.cs

using System.Dynamic;
using System.Globalization;
using System.IO;
using Newtonsoft.Json;
using Newtonsoft.Json.Converters;

namespace System.Web.Mvc
{
    public sealed class JsonDotNetValueProviderFactory : ValueProviderFactory
    {
       public override IValueProvider GetValueProvider(ControllerContext controllerContext)
       {
            if (controllerContext == null)
                throw new ArgumentNullException("controllerContext");
            
            if (!controllerContext.HttpContext.Request.ContentType.StartsWith("application/json", StringComparison.OrdinalIgnoreCase))
                return null;

            var reader = new StreamReader(controllerContext.HttpContext.Request.InputStream);
            var bodyText = reader.ReadToEnd();

            return String.IsNullOrEmpty(bodyText) ? null : new DictionaryValueProvider<object>(JsonConvert.DeserializeObject<ExpandoObject>(bodyText, new ExpandoObjectConverter()) , CultureInfo.CurrentCulture);
        }
    }
}

There's a better solution available in the link. It does not use ReadToEnd, thus saving memory. Follow AdaskoTheBeAsT's comments and make the changes to JsonSerializer.CreateDefault too.
https://json.codeplex.com/discussions/347099