Code Challenge in PKCE

chde_challenge.js

// This code works on the Web Browser, because it uses Web Crypto API.

const codeVerifierLength = 43;
let codeVerifier = '';
const characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-._~';
for (let i = 0; i < codeVerifierLength; i++) {
  codeVerifier += characters.charAt(Math.floor(Math.random() * characters.length));
}

async function generateCodeChallenge(codeVerifier) {
  let digest = await crypto.subtle.digest(
    "SHA-256", new TextEncoder().encode(codeVerifier)
  );

  return btoa(String.fromCharCode(...new Uint8Array(digest))).
    replace(/=/g, '').replace(/\+/g, '-').replace(/\//g, '_');
}

const codeChallenge = await generateCodeChallenge(codeVerifier);

console.log(`Code Verifier : ${codeVerifier}`);
console.log(`Code Challenge: ${codeChallenge}`);

code_challenge.fsi

open System
open System.Linq

let codeVerifierLength = 43
let random = Random()
let chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-._~"
let codeVerifier =
    Enumerable.Repeat(chars, codeVerifierLength).
        Select(fun s -> s.[random.Next(s.Length)]) |>
    String.Concat

let codeChallenge =
    codeVerifier |>
    System.Text.Encoding.UTF8.GetBytes |>
    System.Security.Cryptography.SHA256.Create().ComputeHash |>
    System.Convert.ToBase64String |>
    fun x -> x.Replace("=", "").Replace("+", "-").Replace("/", "_")

printfn "Code Verifier : %s" codeVerifier
printfn "Code Challenge: %s" codeChallenge

code_challenge.py

import base64
import hashlib
import random
import string

code_verifier_length = 43
code_verifier        = ''.join(random.choice(string.ascii_letters + string.digits + '-._~')\
    for i in range(code_verifier_length))

code_challenge = base64.urlsafe_b64encode(hashlib.sha256(code_verifier.encode()).digest()).\
    decode().replace("=", "").replace("+", "-").replace("/", "_")

print("Code Verifier :", code_verifier)
print("Code Challenge:", code_challenge)

code_challenge.rb

require 'digest'
require 'base64'

code_verifier_length = 43
o = ([('a'..'z'), ('A'..'Z'), ('0'..'9')].map(&:to_a) + %w[- _ . ~]).flatten
code_verifier = (0...code_verifier_length).map { o[rand(o.length)] }.join

code_challenge = Base64.urlsafe_encode64(Digest::SHA256.digest(code_verifier)).
  delete('=').gsub('+', '-').gsub('/', '_')

puts "Code Verifier : #{code_verifier}"
puts "Code Challenge: #{code_challenge}"

code_challenge.sh

CODE_VERIFIER_LENGTH=43
CODE_VERIFIER=`cat /dev/urandom | LC_CTYPE=C tr -dc 'a-zA-Z0-9\-._~' | fold -w $CODE_VERIFIER_LENGTH | head -n 1`

CODE_CHALLENGE=`echo -n $CODE_VERIFIER | openssl dgst -sha256 -binary | openssl base64 -A | tr -d '=' | tr '/+' '_-'`

echo "Code Verifier :" $CODE_VERIFIER
echo "Code Challenge:" $CODE_CHALLENGE