OAuth 2.1 deprecates the Implicit Grant flow and mandates Proof Key for Code Exchange (PKCE) for all public clients. Learn how to implement stateless RS256 JWT validation, JWKS key rotation, and multi-tenant security filters in Spring Security 6.
1. Proof Key for Code Exchange (PKCE) Protocol Flow
// 1. Generate High-Entropy Code Verifier
const codeVerifier = crypto.randomUUID() + crypto.randomUUID();
// 2. Compute SHA-256 Code Challenge
async function generateCodeChallenge(verifier) {
const encoder = new TextEncoder();
const data = encoder.encode(verifier);
const digest = await crypto.subtle.digest('SHA-256', data);
return btoa(String.fromCharCode(...new Uint8Array(digest)))
.replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
}