ipiify.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;

namespace WebApplication1
{
    public class Program
    {
        public static void Main(string[] args)
        {
            BuildWebHost(args).Run();
        }

        public static IWebHost BuildWebHost(string[] args) =>
            new WebHostBuilder()
                .UseKestrel()
                .ConfigureLogging((ctx, logging) =>
                {
                    logging.SetMinimumLevel(LogLevel.None);
                })
                .UseStartup<Startup>()
                .Build();
    }

    public class Startup
    {
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            app.Run(async (context) =>
            {
                if (context.Request.Headers.TryGetValue("X-Forwarded-For", out var forward) &&
                    forward.Count != 0)
                {
                    await context.Response.WriteAsync(forward[0]);
                }
                else
                {
                    await context.Response.WriteAsync(context.Connection.RemoteIpAddress.ToString());
                }
            });
        }
    }
}