JQuery stuck at CORS preflight and IIS ghost response

Create PreflightRequestsHandler class where you allow request headers(1) and enable cors before your class(2).

1. public class PreflightRequestsHandler : DelegatingHandler
    {
        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            if (request.Headers.Contains("Origin") && request.Method.Method.Equals("OPTIONS"))
            {
                var response = new HttpResponseMessage { StatusCode = HttpStatusCode.OK };
                // Define and add values to variables: origins, headers, methods (can be global)               
                response.Headers.Add("Access-Control-Allow-Origin", "*");
                response.Headers.Add("Access-Control-Allow-Headers", "content-type");
                response.Headers.Add("Access-Control-Allow-Methods", "*");
                var tsc = new TaskCompletionSource<HttpResponseMessage>();
                tsc.SetResult(response);
                return tsc.Task;
            }
            return base.SendAsync(request, cancellationToken);
        }

    }

2. [EnableCors(origins: "*", headers: "*", methods: "*", exposedHeaders: "X-Custom-Header")]