JsonStatusCodeMiddleWare.cs

public class JsonStatusCodeMiddleWare
    {
        private readonly RequestDelegate _next;
        public JsonStatusCodeMiddleWare(RequestDelegate next)
        {
            _next = next;
        }
        public async Task Invoke(HttpContext context)
        {
            if (context.Response.StatusCode == (int)HttpStatusCode.OK)
            {
                await _next(context);
                return;
            }

            context.Response.ContentType = "application/json";

            string jsonString = "";

            switch (context.Response.StatusCode)
            {
                case (int) HttpStatusCode.NotFound:
                    jsonString = JsonConvert.SerializeObject(new ApiError()
                    {
                        Success = false,
                        ErrorKey = context.Response.StatusCode.ToString(),
                        Message = "Resource does not exist on the server!"
                    });
                    break;
                case (int)HttpStatusCode.Unauthorized:
                    jsonString = JsonConvert.SerializeObject(new ApiError()
                    {
                        Success = false,
                        ErrorKey = context.Response.StatusCode.ToString(),
                        Message = "Requested resource requires authentication!"
                    });
                    break;
                default:
                    break;
            }

            await context.Response.WriteAsync(jsonString, Encoding.UTF8);
        }
    }