kintsugi-programmer Authentication & Authorization Implementation Patterns
Build secure, scalable authentication and authorization systems using industry-standard patterns and modern best practices.
When to Use This Skill
- Implementing user authentication systems
- Securing REST or GraphQL APIs
- Adding OAuth2/social login
- Implementing role-based access control (RBAC)
- Designing session management
- Migrating authentication systems
- Debugging auth issues
- Implementing SSO or multi-tenancy
Core Concepts
1. Authentication vs Authorization
Authentication (AuthN): Who are you?
- Verifying identity (username/password, OAuth, biometrics)
- Issuing credentials (sessions, tokens)
- Managing login/logout
Authorization (AuthZ): What can you do?
- Permission checking
- Role-based access control (RBAC)
- Resource ownership validation
- Policy enforcement
2. Authentication Strategies
Session-Based:
- Server stores session state
- Session ID in cookie
- Traditional, simple, stateful
Token-Based (JWT):
- Stateless, self-contained
- Scales horizontally
- Can store claims
OAuth2/OpenID Connect:
- Delegate authentication
- Social login (Google, GitHub)
- Enterprise SSO
JWT Authentication
Pattern 1: JWT Implementation
// JWT structure: header.payload.signature
import jwt from "jsonwebtoken";
import { Request, Response, NextFunction } from "express";
interface JWTPayload {
userId: string;
email: string;
role: string;
iat: number;
exp: number;
}
// Generate JWT
function generateTokens(userId: string, email: string, role: string) {
const accessToken = jwt.sign(
{ userId, email, role },
process.env.JWT_SECRET!,
{ expiresIn: "15m" }, // Short-lived
);
const refreshToken = jwt.sign(
{ userId },
process.env.JWT_REFRESH_SECRET!,
{ expiresIn: "7d" }, // Long-lived
);
return { accessToken, refreshToken };
}
// Verify JWT
function verifyToken(token: string): JWTPayload {
try {
return jwt.verify(token, process.env.JWT_SECRET!) as JWTPayload;
} catch (error) {
if (error instanceof jwt.TokenExpiredError) {
throw new Error("Token expired");
}
if (error instanceof jwt.JsonWebTokenError) {
throw new Error("Invalid token");
}
throw error;
}
}
// Middleware
function authenticate(req: Request, res: Response, next: NextFunction) {
const authHeader = req.headers.authorization;
if (!authHeader?.startsWith("Bearer ")) {
return res.status(401).json({ error: "No token provided" });
}
const token = authHeader.substring(7);
try {
const payload = verifyToken(token);
req.user = payload; // Attach user to request
next();
} catch (error) {
return res.status(401).json({ error: "Invalid token" });
}
}
// Usage
app.get("/api/profile", authenticate, (req, res) => {
res.json({ user: req.user });
});
Pattern 2: Refresh Token Flow
interface StoredRefreshToken {
token: string;
userId: string;
expiresAt: Date;
createdAt: Date;
}
class RefreshTokenService {
// Store refresh token in database
async storeRefreshToken(userId: string, refreshToken: string) {
const expiresAt = new Date(Date.now() + 7 * 24 * 60 * 60 * 1000);
await db.refreshTokens.create({
token: await hash(refreshToken), // Hash before storing
userId,
expiresAt,
});
}
// Refresh access token
async refreshAccessToken(refreshToken: string) {
// Verify refresh token
let payload;
try {
payload = jwt.verify(refreshToken, process.env.JWT_REFRESH_SECRET!) as {
userId: string;
};
} catch {
throw new Error("Invalid refresh token");
}
// Check if token exists in database
const storedToken = await db.refreshTokens.findOne({
where: {
token: await hash(refreshToken),
userId: payload.userId,
expiresAt: { $gt: new Date() },
},
});
if (!storedToken) {
throw new Error("Refresh token not found or expired");
}
// Get user
const user = await db.users.findById(payload.userId);
if (!user) {
throw new Error("User not found");
}
// Generate new access token
const accessToken = jwt.sign(
{ userId: user.id, email: user.email, role: user.role },
process.env.JWT_SECRET!,
{ expiresIn: "15m" },
);
return { accessToken };
}
// Revoke refresh token (logout)
async revokeRefreshToken(refreshToken: string) {
await db.refreshTokens.deleteOne({
token: await hash(refreshToken),
});
}
// Revoke all user tokens (logout all devices)
async revokeAllUserTokens(userId: string) {
await db.refreshTokens.deleteMany({ userId });
}
}
// API endpoints
app.post("/api/auth/refresh", async (req, res) => {
const { refreshToken } = req.body;
try {
const { accessToken } =
await refreshTokenService.refreshAccessToken(refreshToken);
res.json({ accessToken });
} catch (error) {
res.status(401).json({ error: "Invalid refresh token" });
}
});
app.post("/api/auth/logout", authenticate, async (req, res) => {
const { refreshToken } = req.body;
await refreshTokenService.revokeRefreshToken(refreshToken);
res.json({ message: "Logged out successfully" });
});
Session-Based Authentication
Pattern 1: Express Session
import session from "express-session";
import RedisStore from "connect-redis";
import { createClient } from "redis";
// Setup Redis for session storage
const redisClient = createClient({
url: process.env.REDIS_URL,
});
await redisClient.connect();
app.use(
session({
store: new RedisStore({ client: redisClient }),
secret: process.env.SESSION_SECRET!,
resave: false,
saveUninitialized: false,
cookie: {
secure: process.env.NODE_ENV === "production", // HTTPS only
httpOnly: true, // No JavaScript access
maxAge: 24 * 60 * 60 * 1000, // 24 hours
sameSite: "strict", // CSRF protection
},
}),
);
// Login
app.post("/api/auth/login", async (req, res) => {
const { email, password } = req.body;
const user = await db.users.findOne({ email });
if (!user || !(await verifyPassword(password, user.passwordHash))) {
return res.status(401).json({ error: "Invalid credentials" });
}
// Store user in session
req.session.userId = user.id;
req.session.role = user.role;
res.json({ user: { id: user.id, email: user.email, role: user.role } });
});
// Session middleware
function requireAuth(req: Request, res: Response, next: NextFunction) {
if (!req.session.userId) {
return res.status(401).json({ error: "Not authenticated" });
}
next();
}
// Protected route
app.get("/api/profile", requireAuth, async (req, res) => {
const user = await db.users.findById(req.session.userId);
res.json({ user });
});
// Logout
app.post("/api/auth/logout", (req, res) => {
req.session.destroy((err) => {
if (err) {
return res.status(500).json({ error: "Logout failed" });
}
res.clearCookie("connect.sid");
res.json({ message: "Logged out successfully" });
});
});
OAuth2 / Social Login
Pattern 1: OAuth2 with Passport.js
import passport from "passport";
import { Strategy as GoogleStrategy } from "passport-google-oauth20";
import { Strategy as GitHubStrategy } from "passport-github2";
// Google OAuth
passport.use(
new GoogleStrategy(
{
clientID: process.env.GOOGLE_CLIENT_ID!,
clientSecret: process.env.GOOGLE_CLIENT_SECRET!,
callbackURL: "/api/auth/google/callback",
},
async (accessToken, refreshToken, profile, done) => {
try {
// Find or create user
let user = await db.users.findOne({
googleId: profile.id,
});
if (!user) {
user = await db.users.create({
googleId: profile.id,
email: profile.emails?.[0]?.value,
name: profile.displayName,
avatar: profile.photos?.[0]?.value,
});
}
return done(null, user);
} catch (error) {
return done(error, undefined);
}
},
),
);
// Routes
app.get(
"/api/auth/google",
passport.authenticate("google", {
scope: ["profile", "email"],
}),
);
app.get(
"/api/auth/google/callback",
passport.authenticate("google", { session: false }),
(req, res) => {
// Generate JWT
const tokens = generateTokens(req.user.id, req.user.email, req.user.role);
// Redirect to frontend with token
res.redirect(
`${process.env.FRONTEND_URL}/auth/callback?token=${tokens.accessToken}`,
);
},
);
Authorization Patterns
Pattern 1: Role-Based Access Control (RBAC)
enum Role {
USER = "user",
MODERATOR = "moderator",
ADMIN = "admin",
}
const roleHierarchy: Record<Role, Role[]> = {
[Role.ADMIN]: [Role.ADMIN, Role.MODERATOR, Role.USER],
[Role.MODERATOR]: [Role.MODERATOR, Role.USER],
[Role.USER]: [Role.USER],
};
function hasRole(userRole: Role, requiredRole: Role): boolean {
return roleHierarchy[userRole].includes(requiredRole);
}
// Middleware
function requireRole(...roles: Role[]) {
return (req: Request, res: Response, next: NextFunction) => {
if (!req.user) {
return res.status(401).json({ error: "Not authenticated" });
}
if (!roles.some((role) => hasRole(req.user.role, role))) {
return res.status(403).json({ error: "Insufficient permissions" });
}
next();
};
}
// Usage
app.delete(
"/api/users/:id",
authenticate,
requireRole(Role.ADMIN),
async (req, res) => {
// Only admins can delete users
await db.users.delete(req.params.id);
res.json({ message: "User deleted" });
},
);
Pattern 2: Permission-Based Access Control
enum Permission {
READ_USERS = "read:users",
WRITE_USERS = "write:users",
DELETE_USERS = "delete:users",
READ_POSTS = "read:posts",
WRITE_POSTS = "write:posts",
}
const rolePermissions: Record<Role, Permission[]> = {
[Role.USER]: [Permission.READ_POSTS, Permission.WRITE_POSTS],
[Role.MODERATOR]: [
Permission.READ_POSTS,
Permission.WRITE_POSTS,
Permission.READ_USERS,
],
[Role.ADMIN]: Object.values(Permission),
};
function hasPermission(userRole: Role, permission: Permission): boolean {
return rolePermissions[userRole]?.includes(permission) ?? false;
}
function requirePermission(...permissions: Permission[]) {
return (req: Request, res: Response, next: NextFunction) => {
if (!req.user) {
return res.status(401).json({ error: "Not authenticated" });
}
const hasAllPermissions = permissions.every((permission) =>
hasPermission(req.user.role, permission),
);
if (!hasAllPermissions) {
return res.status(403).json({ error: "Insufficient permissions" });
}
next();
};
}
// Usage
app.get(
"/api/users",
authenticate,
requirePermission(Permission.READ_USERS),
async (req, res) => {
const users = await db.users.findAll();
res.json({ users });
},
);
Pattern 3: Resource Ownership
// Check if user owns resource
async function requireOwnership(
resourceType: "post" | "comment",
resourceIdParam: string = "id",
) {
return async (req: Request, res: Response, next: NextFunction) => {
if (!req.user) {
return res.status(401).json({ error: "Not authenticated" });
}
const resourceId = req.params[resourceIdParam];
// Admins can access anything
if (req.user.role === Role.ADMIN) {
return next();
}
// Check ownership
let resource;
if (resourceType === "post") {
resource = await db.posts.findById(resourceId);
} else if (resourceType === "comment") {
resource = await db.comments.findById(resourceId);
}
if (!resource) {
return res.status(404).json({ error: "Resource not found" });
}
if (resource.userId !== req.user.userId) {
return res.status(403).json({ error: "Not authorized" });
}
next();
};
}
// Usage
app.put(
"/api/posts/:id",
authenticate,
requireOwnership("post"),
async (req, res) => {
// User can only update their own posts
const post = await db.posts.update(req.params.id, req.body);
res.json({ post });
},
);
Security Best Practices
Pattern 1: Password Security
import bcrypt from "bcrypt";
import { z } from "zod";
// Password validation schema
const passwordSchema = z
.string()
.min(12, "Password must be at least 12 characters")
.regex(/[A-Z]/, "Password must contain uppercase letter")
.regex(/[a-z]/, "Password must contain lowercase letter")
.regex(/[0-9]/, "Password must contain number")
.regex(/[^A-Za-z0-9]/, "Password must contain special character");
// Hash password
async function hashPassword(password: string): Promise<string> {
const saltRounds = 12; // 2^12 iterations
return bcrypt.hash(password, saltRounds);
}
// Verify password
async function verifyPassword(
password: string,
hash: string,
): Promise<boolean> {
return bcrypt.compare(password, hash);
}
// Registration with password validation
app.post("/api/auth/register", async (req, res) => {
try {
const { email, password } = req.body;
// Validate password
passwordSchema.parse(password);
// Check if user exists
const existingUser = await db.users.findOne({ email });
if (existingUser) {
return res.status(400).json({ error: "Email already registered" });
}
// Hash password
const passwordHash = await hashPassword(password);
// Create user
const user = await db.users.create({
email,
passwordHash,
});
// Generate tokens
const tokens = generateTokens(user.id, user.email, user.role);
res.status(201).json({
user: { id: user.id, email: user.email },
...tokens,
});
} catch (error) {
if (error instanceof z.ZodError) {
return res.status(400).json({ error: error.errors[0].message });
}
res.status(500).json({ error: "Registration failed" });
}
});
Pattern 2: Rate Limiting
import rateLimit from "express-rate-limit";
import RedisStore from "rate-limit-redis";
// Login rate limiter
const loginLimiter = rateLimit({
store: new RedisStore({ client: redisClient }),
windowMs: 15 * 60 * 1000, // 15 minutes
max: 5, // 5 attempts
message: "Too many login attempts, please try again later",
standardHeaders: true,
legacyHeaders: false,
});
// API rate limiter
const apiLimiter = rateLimit({
windowMs: 60 * 1000, // 1 minute
max: 100, // 100 requests per minute
standardHeaders: true,
});
// Apply to routes
app.post("/api/auth/login", loginLimiter, async (req, res) => {
// Login logic
});
app.use("/api/", apiLimiter);
Best Practices
- Never Store Plain Passwords: Always hash with bcrypt/argon2
- Use HTTPS: Encrypt data in transit
- Short-Lived Access Tokens: 15-30 minutes max
- Secure Cookies: httpOnly, secure, sameSite flags
- Validate All Input: Email format, password strength
- Rate Limit Auth Endpoints: Prevent brute force attacks
- Implement CSRF Protection: For session-based auth
- Rotate Secrets Regularly: JWT secrets, session secrets
- Log Security Events: Login attempts, failed auth
- Use MFA When Possible: Extra security layer
Common Pitfalls
- Weak Passwords: Enforce strong password policies
- JWT in localStorage: Vulnerable to XSS, use httpOnly cookies
- No Token Expiration: Tokens should expire
- Client-Side Auth Checks Only: Always validate server-side
- Insecure Password Reset: Use secure tokens with expiration
- No Rate Limiting: Vulnerable to brute force
- Trusting Client Data: Always validate on server