NotAcceptableResult.cs

using System.Net;
    using System.Net.Http;
    using System.Threading;
    using System.Threading.Tasks;
    using System.Web.Http;

    public class NotAcceptableResult : IHttpActionResult
    {
        private readonly HttpRequestMessage request;

        public NotAcceptableResult(HttpRequestMessage request)
        {
            this.request = request;
        }

        public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
        {
            var response = this.request.CreateResponse(HttpStatusCode.NotAcceptable);
            return Task.FromResult(response);
        }
    }
    
    
    public static class ApiControllerExtensions
    {
        public static NotAcceptableResult NotAcceptable(this ApiController controller)
        {
            return new NotAcceptableResult(controller.Request);
        }
    }