WebApiConfig.cs

 public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            // Web API configuration and services
            // Configure Web API to use only bearer token authentication.
            config.SuppressDefaultHostAuthentication();
            config.Filters.Add(new HostAuthenticationFilter(OAuthDefaults.AuthenticationType));

            config.ConfigureJSONFormatter();

            // Web API routes
            config.MapHttpAttributeRoutes();

            config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );
        }

        private static void ConfigureJSONFormatter(this HttpConfiguration config)
        {
            // remove Json.NET
            // config.Formatters.JsonFormatter.SerializerSettings = new JsonSerializerSettings
            // {
            //     ContractResolver = new CamelCasePropertyNamesContractResolver(),
            //     NullValueHandling = NullValueHandling.Ignore,
            //     DateFormatHandling = DateFormatHandling.IsoDateFormat
            // };

            // use Jil
            config.Formatters.RemoveAt(0);
            config.Formatters.Insert(0, new JilMediaTypeFormatter());
        }
    }