Imported from majiayu000/claude-skill-registry-data (data/auth-security-reviewer/SKILL.md). Install upstream with npx skills add majiayu000/claude-skill-registry-data --skill auth-security-reviewer. Copyright stays with the author.

Auth Security Reviewer

Comprehensive security review of authentication systems.

Session Security Checklist

// ❌ INSECURE Session Configuration
app.use(
  session({
    secret: "weak-secret", // Too simple
    resave: true, // Unnecessary
    saveUninitialized: true, // Creates unnecessary sessions
    cookie: {
      secure: false, // Not HTTPS-only
      httpOnly: false, // Accessible via JavaScript
      sameSite: false, // CSRF vulnerable
      maxAge: 365 * 24 * 60 * 60 * 1000, // 1 year - too long
    },
  })
);

// ✅ SECURE Session Configuration
app.use(
  session({
    secret: process.env.SESSION_SECRET, // From environment
    resave: false,
    saveUninitialized: false,
    name: "sessionId", // Don't use default 'connect.sid'
    cookie: {
      secure: true, // HTTPS only
      httpOnly: true, // No JavaScript access
      sameSite: "strict", // CSRF protection
      maxAge: 24 * 60 * 60 * 1000, // 24 hours
      domain: process.env.COOKIE_DOMAIN,
    },
    store: new RedisStore({
      client: redisClient,
      ttl: 86400,
    }),
  })
);

JWT Security Review

// ❌ INSECURE JWT Implementation
const token = jwt.sign(
  { userId: user.id },
  "weak-secret", // Hardcoded secret
  { algorithm: "HS256" } // No expiration
);

// Store in localStorage
localStorage.setItem("token", token); // XSS vulnerable

// ✅ SECURE JWT Implementation
const token = jwt.sign(
  {
    userId: user.id,
    role: user.role,
    iat: Math.floor(Date.now() / 1000),
  },
  process.env.JWT_SECRET, // Strong secret from env
  {
    algorithm: "HS256",
    expiresIn: "15m", // Short-lived
    issuer: "myapp.com",
    audience: "myapp.com",
  }
);

// Store in httpOnly cookie
res.cookie("accessToken", token, {
  httpOnly: true,
  secure: true,
  sameSite: "strict",
  maxAge: 15 * 60 * 1000,
});

// Refresh token with longer expiry
const refreshToken = jwt.sign(
  { userId: user.id, type: "refresh" },
  process.env.REFRESH_TOKEN_SECRET,
  { expiresIn: "7d" }
);

// Store refresh token in database
await storeRefreshToken(user.id, refreshToken);

CSRF Protection

// Using csurf middleware
import csrf from "csurf";

const csrfProtection = csrf({ cookie: true });

// Apply to state-changing routes
app.post("/api/transfer", csrfProtection, async (req, res) => {
  // Protected from CSRF
  await processTransfer(req.body);
  res.json({ success: true });
});

// Provide CSRF token to frontend
app.get("/api/csrf-token", csrfProtection, (req, res) => {
  res.json({ csrfToken: req.csrfToken() });
});

// Frontend usage
const csrfToken = await fetch("/api/csrf-token").then((r) => r.json());

await fetch("/api/transfer", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    "X-CSRF-Token": csrfToken.csrfToken,
  },
  body: JSON.stringify({ amount: 100 }),
});

Password Security

// ❌ INSECURE Password Handling
const password = req.body.password;
const hash = crypto.createHash("md5").update(password).digest("hex"); // MD5 is broken
await db.user.create({ password: hash });

// ✅ SECURE Password Handling
import bcrypt from "bcrypt";

// Hashing
const saltRounds = 12; // Adjust based on security requirements
const hash = await bcrypt.hash(password, saltRounds);
await db.user.create({ passwordHash: hash });

// Verification
const isValid = await bcrypt.compare(password, user.passwordHash);

// Password requirements
function validatePassword(password: string): boolean {
  return (
    password.length >= 12 &&
    /[A-Z]/.test(password) && // Uppercase
    /[a-z]/.test(password) && // Lowercase
    /[0-9]/.test(password) && // Number
    /[^A-Za-z0-9]/.test(password) // Special char
  );
}

// Check against breached passwords
import { pwnedPassword } from "hibp";

const breachCount = await pwnedPassword(password);
if (breachCount > 0) {
  throw new Error("This password has been found in data breaches");
}

Multi-Factor Authentication

// TOTP-based MFA
import speakeasy from "speakeasy";
import qrcode from "qrcode";

// Generate secret
const secret = speakeasy.generateSecret({
  name: `MyApp (${user.email})`,
  issuer: "MyApp",
});

// Store secret
await db.user.update({
  where: { id: user.id },
  data: {
    mfaSecret: secret.base32,
    mfaEnabled: false, // Not enabled until verified
  },
});

// Generate QR code
const qrCodeUrl = await qrcode.toDataURL(secret.otpauth_url);

// Verify TOTP token
function verifyMFA(token: string, secret: string): boolean {
  return speakeasy.totp.verify({
    secret,
    encoding: "base32",
    token,
    window: 2, // Allow 2 time steps before/after
  });
}

// Backup codes
function generateBackupCodes(): string[] {
  return Array.from({ length: 10 }, () =>
    crypto.randomBytes(4).toString("hex").toUpperCase()
  );
}

Authorization Vulnerabilities

// ❌ INSECURE: Missing authorization check
app.get("/api/users/:id/profile", async (req, res) => {
  const profile = await db.user.findUnique({
    where: { id: req.params.id },
  });
  res.json(profile); // Anyone can access any profile!
});

// ✅ SECURE: Proper authorization
app.get("/api/users/:id/profile", authenticate, async (req, res) => {
  // Check if user can access this profile
  if (req.user.id !== req.params.id && req.user.role !== "ADMIN") {
    return res.status(403).json({ error: "Forbidden" });
  }

  const profile = await db.user.findUnique({
    where: { id: req.params.id },
  });
  res.json(profile);
});

// ❌ INSECURE: IDOR vulnerability
app.delete("/api/orders/:id", async (req, res) => {
  await db.order.delete({ where: { id: req.params.id } });
  res.json({ success: true });
});

// ✅ SECURE: Verify ownership
app.delete("/api/orders/:id", authenticate, async (req, res) => {
  const order = await db.order.findUnique({
    where: { id: req.params.id },
  });

  if (!order) {
    return res.status(404).json({ error: "Not found" });
  }

  if (order.userId !== req.user.id) {
    return res.status(403).json({ error: "Forbidden" });
  }

  await db.order.delete({ where: { id: req.params.id } });
  res.json({ success: true });
});

Session Fixation Prevention

// ❌ INSECURE: Session not regenerated on login
app.post("/login", async (req, res) => {
  const user = await authenticate(req.body);
  req.session.userId = user.id;
  res.json({ success: true });
});

// ✅ SECURE: Regenerate session on login
app.post("/login", async (req, res) => {
  const user = await authenticate(req.body);

  // Regenerate session to prevent fixation
  req.session.regenerate((err) => {
    if (err) return res.status(500).json({ error: "Server error" });

    req.session.userId = user.id;
    res.json({ success: true });
  });
});

// Also regenerate on privilege escalation
app.post("/admin/elevate", async (req, res) => {
  // Verify admin credentials
  await verifyAdminPassword(req.body.password);

  // Regenerate session
  req.session.regenerate((err) => {
    if (err) return res.status(500).json({ error: "Server error" });

    req.session.isAdmin = true;
    res.json({ success: true });
  });
});

Rate Limiting on Auth Endpoints

import rateLimit from "express-rate-limit";

// Strict rate limit for login
const loginLimiter = rateLimit({
  windowMs: 15 * 60 * 1000, // 15 minutes
  max: 5, // 5 attempts
  message: "Too many login attempts, please try again later",
  standardHeaders: true,
  legacyHeaders: false,
  // Use IP + username for more granular limiting
  keyGenerator: (req) => `${req.ip}-${req.body.email}`,
});

app.post("/api/login", loginLimiter, async (req, res) => {
  // Login logic
});

// Even stricter for password reset
const resetLimiter = rateLimit({
  windowMs: 60 * 60 * 1000, // 1 hour
  max: 3,
  message: "Too many password reset attempts",
});

app.post("/api/password-reset", resetLimiter, async (req, res) => {
  // Password reset logic
});

Security Testing

// tests/auth-security.test.ts
describe("Auth Security", () => {
  describe("Session Security", () => {
    it("should set httpOnly cookie", async () => {
      const response = await request(app)
        .post("/api/login")
        .send({ email: "test@example.com", password: "password123" });

      const cookie = response.headers["set-cookie"][0];
      expect(cookie).toContain("HttpOnly");
      expect(cookie).toContain("Secure");
      expect(cookie).toContain("SameSite=Strict");
    });

    it("should regenerate session on login", async () => {
      const agent = request.agent(app);

      // Get initial session
      await agent.get("/");
      const initialCookie = agent.jar.getCookie("sessionId");

      // Login
      await agent.post("/api/login").send({
        email: "test@example.com",
        password: "password123",
      });

      const loginCookie = agent.jar.getCookie("sessionId");

      // Session ID should change
      expect(loginCookie.value).not.toBe(initialCookie.value);
    });
  });

  describe("CSRF Protection", () => {
    it("should reject requests without CSRF token", async () => {
      await request(app)
        .post("/api/transfer")
        .send({ amount: 100 })
        .expect(403);
    });

    it("should accept requests with valid CSRF token", async () => {
      const { csrfToken } = await request(app)
        .get("/api/csrf-token")
        .then((r) => r.body);

      await request(app)
        .post("/api/transfer")
        .set("X-CSRF-Token", csrfToken)
        .send({ amount: 100 })
        .expect(200);
    });
  });

  describe("Authorization", () => {
    it("should prevent IDOR attacks", async () => {
      const user1 = await createUser();
      const user2 = await createUser();

      const token1 = generateToken(user1);

      // Try to access user2's profile with user1's token
      await request(app)
        .get(`/api/users/${user2.id}/profile`)
        .set("Authorization", `Bearer ${token1}`)
        .expect(403);
    });
  });
});

Best Practices

1. Regenerate sessions: On login and privilege changes
2. Short-lived tokens: 15min access, 7-day refresh
3. CSRF protection: All state-changing operations
4. Rate limiting: Prevent brute force
5. Secure cookies: HttpOnly, Secure, SameSite
6. MFA: For sensitive operations
7. Audit logs: Track authentication events

Output Checklist

• Session configuration reviewed
• JWT implementation secured
• CSRF protection enabled
• Password hashing with bcrypt
• MFA implementation (if required)
• Authorization checks on all endpoints
• Session fixation prevention
• Rate limiting on auth endpoints
• Security tests written
• Audit logging configured