OAuth 2.0 Authorization Code with PKCE for public clients

                  import { sha256 } from './crypto.js';

const codeVerifier = crypto.randomUUID() + crypto.randomUUID();
sessionStorage.setItem('pkce_verifier', codeVerifier);

const digest = await sha256(codeVerifier);
const codeChallenge = btoa(String.fromCharCode(...new Uint8Array(digest)))
  .replace(/\+/g, '-')
  .replace(/\//g, '_')
  .replace(/=+$/, '');

location.href = `https://auth.example.com/oauth/authorize?response_type=code&client_id=spa-client&code_challenge_method=S256&code_challenge=${codeChallenge}`;