public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        //.....
        app.UseExceptionHandler(appBuilder =>
        {
            appBuilder.Run(async context =>
            {
                context.Response.StatusCode = 500;

                var exceptionFeature = context.Features.Get<IExceptionHandlerFeature>();
                if (exceptionFeature != null)
                {
                    var nLoggerFactory = loggerFactory.AddNLog();
                    var logger = nLoggerFactory.CreateLogger("Global Exception logger");
                    using (var reader = new StreamReader(context.Request.Body))
                    {
                        logger.LogError(500,
                            $"Request : {reader.ReadToEnd()} {Environment.NewLine} Exception : {exceptionFeature.Error.ToString()}");
                    }
                    await context.Response.WriteAsync(exceptionFeature.Error.ToString());

                    return;
                }
                await context.Response.WriteAsync("An un-expected server error has happened!");
            });
        });
        //.....
    }