oauth-implementation

# OAuth Implementation Implement OAuth 2.0 and OpenID Connect for secure authentication. ## OAuth 2.0 Flows | Flow | Use Case | |------|----------| | Authorization Code | Web apps (most secure) | | Authorization Code + PKCE | SPAs, mobile apps | | Client Credentials | Service-to-service | | Refresh Token | Session renewal | ## Authorization Code Flow (Express) ```javascript const express = require('express'); const jwt = require('jsonwebtoken'); // Step 1: Redirect to authorization app.get('/auth/login', (req, res) => { const state = crypto.randomBytes(16).toString('hex'); req.session.oauthState = state; const params = new URLSearchParams({ client_id: process.env.CLIENT_ID, redirect_uri: process.env.REDIRECT_URI, response_type: 'code', scope: 'openid profile email', state }); res.redirect(`${PROVIDER_URL}/authorize?${params}`); }); // Step 2: Handle callback app.get('/auth/callback', async (req, res) => { if (req.query.state !== req.session.oauthState) { return res.status(400).json({ error: 'Invalid state' }); } const tokenResponse = await fetch(`${PROVIDER_URL}/token`, { method: 'POST', headers: { 'Content-Type': 'application/x-www-form-urlencoded' }, body: new URLSearchParams({ grant_type: 'authorization_code', code: req.query.code, redirect_uri: process.env.REDIRECT_URI, client_id: process.env.CLIENT_ID, client_secret: process.env.CLIENT_SECRET }) }); const tokens = await t...