using System;

using System.Security.Cryptography;

using System.Text;

public class Program

{

    public static void Main()

    {

        string codeVerifier = "XE8hKl6ZRPBUItYZyJlwXxYwDgN9qhCIk7idPDmZqq0";

        using (var sha = SHA256.Create())

            {

                var bytes = Encoding.UTF8.GetBytes(codeVerifier);

                var hash = sha.ComputeHash(bytes);

                var result = Convert.ToBase64String(hash)

                    //Change Base64 to Base64Url https://stackoverflow.com/a/55389212

                    //In Java can be used: https://stackoverflow.com/a/38287029

                    .TrimEnd('=')

                    .Replace('+', '-')

                    .Replace('/', '_');

                Console.WriteLine("For codeVerifier = {0}", codeVerifier);

                Console.WriteLine("CodeChallenge need be  : k-Qajp6QQxZdnUX72MjKp4MKf_ZVSL9jnR4_nXrBwA4");

                Console.WriteLine("CodeChallenge Generated: {0}", result);

            }

    }

}