Security Best Practices

When to use this skill

• New project: consider security from the start
• Security audit: inspect and fix vulnerabilities
• Public API: harden APIs accessible externally
• Compliance: comply with GDPR, PCI-DSS, etc.

Instructions

Step 1: Enforce HTTPS and security headers

Express.js security middleware:

import express from 'express';
import helmet from 'helmet';
import rateLimit from 'express-rate-limit';

const app = express();

// Helmet: automatically set security headers
app.use(helmet({
  contentSecurityPolicy: {
    directives: {
      defaultSrc: ["'self'"],
      scriptSrc: ["'self'", "'unsafe-inline'", "https://trusted-cdn.com"],
      styleSrc: ["'self'", "'unsafe-inline'"],
      imgSrc: ["'self'", "data:", "https:"],
      connectSrc: ["'self'", "https://api.example.com"],
      fontSrc: ["'self'", "https:", "data:"],
      objectSrc: ["'none'"],
      mediaSrc: ["'self'"],
      frameSrc: ["'none'"],
    },
  },
  hsts: {
    maxAge: 31536000,
    includeSubDomains: true,
    preload: true
  }
}));

// Enforce HTTPS
app.use((req, res, next) => {
  if (process.env.NODE_ENV === 'production' && !req.secure) {
    return res.redirect(301, `https://${req.headers.host}${req.url}`);
  }
  next();
});

// Rate limiting (DDoS prevention)
const limiter = rateLimit({
  windowMs: 15 * 60 * 1000, // 15 minutes
  max: 100, // max 100 requests per IP
  message: 'Too many requests from this IP, please try again later.',
  standardHeaders: true,
  legacyHeaders: false,
});

app.use('/api/', limiter);

// Stricter for auth endpoints
const authLimiter = rateLimit({
  windowMs: 15 * 60 * 1000,
  max: 5, // only 5 times per 15 minutes
  skipSuccessfulRequests: true // do not count successful requests
});

app.use('/api/auth/login', authLimiter);

Step 2: Input validation (SQL Injection, XSS prevention)

Joi validation:

import Joi from 'joi';

const userSchema = Joi.object({
  email: Joi.string().email().required(),
  password: Joi.string().min(8).pattern(/^(?=.*[A-Z])(?=.*[a-z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]/).required(),
  name: Joi.string().min(2).max(50).required()
});

app.post('/api/users', async (req, res) => {
  // 1. Validate input
  const { error, value } = userSchema.validate(req.body);

  if (error) {
    return res.status(400).json({ error: error.details[0].message });
  }

  // 2. Prevent SQL Injection: Parameterized Queries
  // ❌ Bad example
  // db.query(`SELECT * FROM users WHERE email = '${email}'`);

  // ✅ Good example
  const user = await db.query('SELECT * FROM users WHERE email = ?', [value.email]);

  // 3. Prevent XSS: Output Encoding
  // React/Vue escape automatically; otherwise use a library
  import DOMPurify from 'isomorphic-dompurify';
  const sanitized = DOMPurify.sanitize(userInput);

  res.json({ user: sanitized });
});

Step 3: Prevent CSRF

CSRF Token:

import csrf from 'csurf';
import cookieParser from 'cookie-parser';

app.use(cookieParser());

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

// Provide CSRF token
app.