app.Use(async (context, next) =>
            {
                context.Response.OnStarting(() =>
                {
                    var origin = context.Request.Headers["Origin"];
                    if (origin.Count > 0)
                    {
                        if (context.Request.Method == System.Net.Http.HttpMethod.Options.Method)
                            context.Response.Headers.Add("Access-Control-Allow-Headers", "*");
                        context.Response.Headers.Add("Access-Control-Allow-Origin", origin);
                        context.Response.Headers.Add("Access-Control-Allow-Credentials", new string[] { "true" });
                    }
                    return System.Threading.Tasks.Task.CompletedTask;
                });
                await next();
            });