JsonDotNetValueProviderFactory.cs

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);
    }
 }