Example parse status code by brute force web pages. C#

SourceBFParser.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Threading.Tasks;

namespace ParseCorrectPages
{
    class Source
    {
        public List<string> CorrectUrlList { get; private set; } = new();
        private readonly string _baseUrl;

        private enum Letters
        {
            start = 48,
            end = 57
        }

        public Source(string baseUrl)
        {
            if (!Uri.IsWellFormedUriString(baseUrl, UriKind.Absolute))
                throw new Exception("Incorrect URL");

            _baseUrl = baseUrl;
        }

        public void PrintValidUrl()
        {
            Console.WriteLine("\t***\nCorrect urls:");
            CorrectUrlList.ForEach(i => Console.WriteLine(i));
            Console.WriteLine("\nend\n\t***");
        }

        public Task BruteForce(int CountOfRandomLetters = 3, char stamph = '~')
        {
            int replaceIdx = _baseUrl.IndexOf(stamph);
            if (replaceIdx == -1 || CountOfRandomLetters < 0 || CountOfRandomLetters > int.MaxValue)
                return Task.CompletedTask;

            List<char> countOfLetters = Enumerable.Range(1, CountOfRandomLetters).Select(i => (char)Letters.start).ToList();
            List<Task> taskList = new();
            while (true)
                for (int l = 0; l < countOfLetters.Count; l++)
                {
                    if (countOfLetters[l] >= (char)Letters.end)
                    {
                        if ((l + 1) >= countOfLetters.Count)
                        {
                            Task.WaitAll(taskList.ToArray());
                            return Task.CompletedTask;
                        }
                        countOfLetters[l] = (char)Letters.start;

                        if (l + 1 < countOfLetters.Count)
                            countOfLetters[l + 1]++;
                    }
                    string currentUrl = _baseUrl[0..replaceIdx] + string.Join("", countOfLetters) + _baseUrl[(replaceIdx + 1)..];
                    taskList.Add(Task.Factory.StartNew(() =>
                    {
                        HttpWebRequest HWReq = WebRequest.Create(currentUrl) as HttpWebRequest;
                        HWReq.AllowAutoRedirect = false;
                        HWReq.UserAgent = "secret.agent";
                        try
                        {
                            using HttpWebResponse HWRes = (HttpWebResponse)HWReq.GetResponse();
                            if (HWRes.StatusCode == HttpStatusCode.OK)
                            {
                                CorrectUrlList.Add(currentUrl);
                                Console.WriteLine($"OK: {currentUrl}");
                            }
                            else
                            {
                                Console.WriteLine($"Fail: {currentUrl}");
                            }
                        }
                        catch (Exception e) { Console.WriteLine(e.Message); }
                    }));
                    countOfLetters[0]++;
                }
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                Source src = new(@"https://store.steampowered.com/app/~");
                src.BruteForce(6);
                src.PrintValidUrl();
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }
        }
    }
}