Kestrel programmatic rebinding

Program.cs

// This shows how to change Kestrel's bindings programmatically through the IConfiguraiton abstraction.
// TFM: .NET 5.0

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using System;
using System.Threading;

namespace WebApplication85
{
    public class Program
    {
        private static IConfigurationRoot KestrelConfig;

        public static void Main(string[] args)
        {
            var configBuilder = new ConfigurationBuilder();
            // A custom source/provider is required because the InMemory one doesn't support key removal.
            configBuilder.Add(new MutableSource());
            KestrelConfig = configBuilder.Build();

            var timer = new Timer(_ =>
            {
                var port = new Random().Next(5000, 5005);
                var key = $"Endpoints:{port}:Url";
                var url = KestrelConfig[key];
                if (string.IsNullOrEmpty(url))
                {
                    url = $"https://*:" + port;
                    KestrelConfig[key] = url;
                    Console.WriteLine("Adding: " + url);
                }
                else
                {
                    KestrelConfig[key] = null;
                    Console.WriteLine("Removing: " + url);
                }

                Console.WriteLine(KestrelConfig.GetDebugView());

                KestrelConfig.Reload();

            }, null, TimeSpan.FromSeconds(2), TimeSpan.FromSeconds(3));

            CreateHostBuilder(args).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                    webBuilder.ConfigureKestrel(kOptions =>
                    {
                        // We need at least one binding to actually start the server.
                        // This could also be in config.
                        kOptions.ListenAnyIP(4999, listenOptions =>
                        {
                            listenOptions.UseHttps();
                        });

                        kOptions.ConfigureHttpsDefaults(httpsOptions =>
                        {
                            // Set up https for config based endpoints. Defaults to the dev certificate.
                        });

                        kOptions.Configure(KestrelConfig, reloadOnChange: true);
                    });
                });

        private class MutableProvider : ConfigurationProvider
        {
            public override void Set(string key, string value)
            {
                if (value == null)
                {
                    Data.Remove(key);
                }
                else
                {
                    Data[key] = value;
                }
            }
        }

        private class MutableSource : IConfigurationSource
        {
            public IConfigurationProvider Build(IConfigurationBuilder builder)
            {
                return new MutableProvider();
            }
        }
    }
}