api-security-best-practices

Guide developers in building secure APIs by implementing authentication, authorization, input validation, rate limiting, and protection against common vulnerabilities. This skill covers security patterns for REST, GraphQL, and WebSocket APIs.

• Use when designing new API endpoints
• Use when securing existing APIs
• Use when implementing authentication and authorization
• Use when protecting against API attacks (injection, DDoS, etc.)
• Use when conducting API security reviews
• Use when preparing for security audits
• Use when implementing rate limiting and throttling
• Use when handling sensitive data in APIs

Step 1: Authentication & Authorization

I'll help you implement secure authentication:

• Choose authentication method (JWT, OAuth 2.0, API keys)
• Implement token-based authentication
• Set up role-based access control (RBAC)
• Secure session management
• Implement multi-factor authentication (MFA)

Step 2: Input Validation & Sanitization

Protect against injection attacks:

• Validate all input data
• Sanitize user inputs
• Use parameterized queries
• Implement request schema validation
• Prevent SQL injection, XSS, and command injection

Step 3: Rate Limiting & Throttling

Prevent abuse and DDoS attacks:

• Implement rate limiting per user/IP
• Set up API throttling
• Configure request quotas
• Handle rate limit errors gracefully
• Monitor for suspicious activity

Step 4: Data Protection

Secure sensitive data:

• Encrypt data in transit (HTTPS/TLS)
• Encrypt sensitive data at rest
• Implement proper error handling (no data leaks)
• Sanitize error messages
• Use secure headers

Step 5: API Security Testing

Verify security implementation:

• Test authentication and authorization
• Perform penetration testing
• Check for common vulnerabilities (OWASP API Top 10)
• Validate input handling
• Test rate limiting

Example 1: Implementing JWT Authentication

```markdown

Authentication Flow

1. User logs in with credentials
2. Server validates credentials
3. Server generates JWT token
4. Client stores token securely
5. Client sends token with each request
6. Server validates token

Implementation

#### 1. Generate Secure JWT Tokens

\\\`javascript

// auth.js

const jwt = require('jsonwebtoken');

const bcrypt = require('bcrypt');

// Login endpoint

app.post('/api/auth/login', async (req, res) => {

try {

const { email, password } = req.body;

// Validate input

if (!email || !password) {

return res.status(400).json({

error: 'Email and password are required'

});

}

// Find user

const user = await db.user.findUnique({

where: { email }

});

if (!user) {

// Don't reveal if user exists

return res.status(401).json({

error: 'Invalid credentials'

});

}

// Verify password

const validPassword = await bcrypt.compare(

password,

user.passwordHash

);

if (!validPassword) {

return res.status(401).json({

error: 'Invalid credentials'

});

}

// Generate JWT token

const token = jwt.sign(

{

userId: user.id,

email: user.email,

role: user.role

},

process.env.JWT_SECRET,

{

expiresIn: '1h',

issuer: 'your-app',

audience: 'your-app-users'

}

);

// Generate refresh token

const refreshToken = jwt.sign(

{ userId: user.id },

process.env.JWT_REFRESH_SECRET,

{ expiresIn: '7d' }

);

// Store refresh token in database

await db.refreshToken.create({

data: {

token: refreshToken,

userId: user.id,

expiresAt: new Date(Date.now() + 7 24 60 60 1000)

}

});

res.json({

token,

refreshToken,

expiresIn: 3600

});

} catch (error) {

console.error('Login error:', error);

res.status(500).json({

error: 'An error occurred during login'

});

}

});

\\\`

#### 2. Verify JWT Tokens (Middleware)

\\\`javascript

// middleware/auth.js

const jwt = require('jsonwebtoken');

function authenticateToken(req, res, next) {

// Get token from header

const authHeader = req.headers['authorization'];

const token = authHeader && authHeader.split(' ')[1]; // Bearer TOKEN

if (!token) {

return res.status(401).json({

error: 'Access token required'

});

}

// Verify token

jwt.verify(

token,

process.env.JWT_SECRET,

{

issuer: 'your-app',

audience: 'your-app-users'

},

(err, user) => {

if (err) {

if (err.name === 'TokenExpiredError') {

return res.status(401).json({

error: 'Token expired'

});

}

return res.status(403).json({

error: 'Invalid token'

});

}

// Attach user to request

req.user = user;

next();

}

);

}

module.exports = { authenticateToken };

\\\`

#### 3. Protect Routes

\\\`javascript

const { authenticateToken } = require('./middleware/auth');

// Protected route

app.get('/api/user/profile', authenticateToken, async (req, res) => {

try {

const user = await db.user.findUnique({

where: { id: req.user.userId },

select: {

id: true,

email: true,

name: true,

// Don't return passwordHash

}

});

res.json(user);

} catch (error) {

res.status(500).json({ error: 'Server error' });

}

});

\\\`

#### 4. Implement Token Refresh

\\\`javascript

app.post('/api/auth/refresh', async (req, res) => {

const { refreshToken } = req.body;

if (!refreshToken) {

return res.status(401).json({

error: 'Refresh token required'

});

}

try {

// Verify refresh token

const decoded = jwt.verify(

refreshToken,

process.env.JWT_REFRESH_SECRET

);

// Check if refresh token exists in database

const storedToken = await db.refreshToken.findFirst({

where: {

token: refreshToken,

userId: decoded.userId,

expiresAt: { gt: new Date() }

}

});

if (!storedToken) {

return res.status(403).json({

error: 'Invalid refresh token'

});

}

// Generate new access token

const user = await db.user.findUnique({

where: { id: decoded.userId }

});

const newToken = jwt.sign(

{

userId: user.id,

email: user.email,

role: user.role

},

process.env.JWT_SECRET,

{ expiresIn: '1h' }

);

res.json({

token: newToken,

expiresIn: 3600

});

} catch (error) {

res.status(403).json({

error: 'Invalid refresh token'

});

}

});

\\\`

Security Best Practices

• ✅ Use strong JWT secrets (256-bit minimum)
• ✅ Set short expiration times (1 hour for access tokens)
• ✅ Implement refresh tokens for long-lived sessions
• ✅ Store refresh tokens in database (can be revoked)
• ✅ Use HTTPS only
• ✅ Don't store sensitive data in JWT payload
• ✅ Validate token issuer and audience
• ✅ Implement token blacklisting for logout

```

Example 2: Input Validation and SQL Injection Prevention

```markdown

The Problem

❌ Vulnerable Code:

\\\`javascript

// NEVER DO THIS - SQL Injection vulnerability

app.get('/api/users/:id', async (req, res) => {

const userId = req.params.id;

// Dangerous: User input directly in query

const query = \SELECT * FROM users WHERE id = '\${userId}'\;

const user = await db.query(query);

res.json(user);

});

// Attack example:

// GET /api/users/1' OR '1'='1

// Returns all users!

\\\`

The Solution

#### 1. Use Parameterized Queries

\\\`javascript

// ✅ Safe: Parameterized query

app.get('/api/users/:id', async (req, res) => {

const userId = req.params.id;

// Validate input first

if (!userId || !/^\d+$/.test(userId)) {

return res.status(400).json({

error: 'Invalid user ID'

});

}

// Use parameterized query

const user = await db.query(

'SELECT id, email, name FROM users WHERE id = $1',

[userId]

);

if (!user) {

return res.status(404).json({

error: 'User not found'

});

}

res.json(user);

});

\\\`

#### 2. Use ORM with Proper Escaping

\\\`javascript

// ✅ Safe: Using Prisma ORM

app.get('/api/users/:id', async (req, res) => {

const userId = parseInt(req.params.id);

if (isNaN(userId)) {

return res.status(400).json({

error: 'Invalid user ID'

});

}

const user = await prisma.user.findUnique({

where: { id: userId },

select: {

id: true,

email: true,

name: true,

// Don't select sensitive fields

}

});

if (!user) {

return res.status(404).json({

error: 'User not found'

});

}

res.json(user);

});

\\\`

#### 3. Implement Request Validation with Zod

\\\`javascript

const { z } = require('zod');

// Define validation schema

const createUserSchema = z.object({

email: z.string().email('Invalid email format'),

password: z.string()

.min(8, 'Password must be at least 8 characters')

.regex(/[A-Z]/, 'Password must contain uppercase letter')

.regex(/[a-z]/, 'Password must contain lowercase letter')

.regex(/[0-9]/, 'Password must contain number'),

name: z.string()

.min(2, 'Name must be at least 2 characters')

.max(100, 'Name too long'),

age: z.number()

.int('Age must be an integer')

.min(18, 'Must be 18 or older')

.max(120, 'Invalid age')

.optional()

});

// Validation middleware

function validateRequest(schema) {

return (req, res, next) => {

try {

schema.parse(req.body);

next();

} catch (error) {

res.status(400).json({

error: 'Validation failed',

details: error.errors

});

}

};

}

// Use validation

app.post('/api/users',

validateRequest(createUserSchema),

async (req, res) => {

// Input is validated at this point

const { email, password, name, age } = req.body;

// Hash password

const passwordHash = await bcrypt.hash(password, 10);

// Create user

const user = await prisma.user.create({

data: {

email,

passwordHash,

name,

age

}

});

// Don't return password hash

const { passwordHash: _, ...userWithoutPassword } = user;

res.status(201).json(userWithoutPassword);

}

);

\\\`

#### 4. Sanitize Output to Prevent XSS

\\\`javascript

const DOMPurify = require('isomorphic-dompurify');

app.post('/api/comments', authenticateToken, async (req, res) => {

const { content } = req.body;

// Validate

if (!content || content.length > 1000) {

return res.status(400).json({

error: 'Invalid comment content'

});

}

// Sanitize HTML to prevent XSS

const sanitizedContent = DOMPurify.sanitize(content, {

ALLOWED_TAGS: ['b', 'i', 'em', 'strong', 'a'],

ALLOWED_ATTR: ['href']

});

const comment = await prisma.comment.create({

data: {

content: sanitizedContent,

userId: req.user.userId

}

});

res.status(201).json(comment);

});

\\\`

Validation Checklist

• [ ] Validate all user inputs
• [ ] Use parameterized queries or ORM
• [ ] Validate data types (string, number, email, etc.)
• [ ] Validate data ranges (min/max length, value ranges)
• [ ] Sanitize HTML content
• [ ] Escape special characters
• [ ] Validate file uploads (type, size, content)
• [ ] Use allowlists, not blocklists

```

Example 3: Rate Limiting and DDoS Protection

```markdown

Why Rate Limiting?

• Prevent brute force attacks
• Protect against DDoS
• Prevent API abuse
• Ensure fair usage
• Reduce server costs

Implementation with Express Rate Limit

\\\`javascript

const rateLimit = require('express-rate-limit');

const RedisStore = require('rate-limit-redis');

const Redis = require('ioredis');

// Create Redis client

const redis = new Redis({

host: process.env.REDIS_HOST,

port: process.env.REDIS_PORT

});

// General API rate limit

const apiLimiter = rateLimit({

store: new RedisStore({

client: redis,

prefix: 'rl:api:'

}),

windowMs: 15 60 1000, // 15 minutes

max: 100, // 100 requests per window

message: {

error: 'Too many requests, please try again later',

retryAfter: 900 // seconds

},

standardHeaders: true, // Return rate limit info in headers

legacyHeaders: false,

// Custom key generator (by user ID or IP)

keyGenerator: (req) => {

return req.user?.userId || req.ip;

}

});

// Strict rate limit for authentication endpoints

const authLimiter = rateLimit({

store: new RedisStore({

client: redis,

prefix: 'rl:auth:'

}),

windowMs: 15 60 1000, // 15 minutes

max: 5, // Only 5 login attempts per 15 minutes

skipSuccessfulRequests: true, // Don't count successful logins

message: {

error: 'Too many login attempts, please try again later',

retryAfter: 900

}

});

// Apply rate limiters

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

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

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

// Custom rate limiter for expensive operations

const expensiveLimiter = rateLimit({

windowMs: 60 60 1000, // 1 hour

max: 10, // 10 requests per hour

message: {

error: 'Rate limit exceeded for this operation'

}

});

app.post('/api/reports/generate',

authenticateToken,

expensiveLimiter,

async (req, res) => {

// Expensive operation

}

);

\\\`

Advanced: Per-User Rate Limiting

\\\`javascript

// Different limits based on user tier

function createTieredRateLimiter() {

const limits = {

free: { windowMs: 60 60 1000, max: 100 },

pro: { windowMs: 60 60 1000, max: 1000 },

enterprise: { windowMs: 60 60 1000, max: 10000 }

};

return async (req, res, next) => {

const user = req.user;

const tier = user?.tier || 'free';

const limit = limits[tier];

const key = \rl:user:\${user.userId}\;

const current = await redis.incr(key);

if (current === 1) {

await redis.expire(key, limit.windowMs / 1000);

}

if (current > limit.max) {

return res.status(429).json({

error: 'Rate limit exceeded',

limit: limit.max,

remaining: 0,

reset: await redis.ttl(key)

});

}

// Set rate limit headers

res.set({

'X-RateLimit-Limit': limit.max,

'X-RateLimit-Remaining': limit.max - current,

'X-RateLimit-Reset': await redis.ttl(key)

});

next();

};

}

app.use('/api/', authenticateToken, createTieredRateLimiter());

\\\`

DDoS Protection with Helmet

\\\`javascript

const helmet = require('helmet');

app.use(helmet({

// Content Security Policy

contentSecurityPolicy: {

directives: {

defaultSrc: ["'self'"],

styleSrc: ["'self'", "'unsafe-inline'"],

scriptSrc: ["'self'"],

imgSrc: ["'self'", 'data:', 'https:']

}

},

// Prevent clickjacking

frameguard: { action: 'deny' },

// Hide X-Powered-By header

hidePoweredBy: true,

// Prevent MIME type sniffing

noSniff: true,

// Enable HSTS

hsts: {

maxAge: 31536000,

includeSubDomains: true,

preload: true

}

}));

\\\`

Rate Limit Response Headers

\\\`

X-RateLimit-Limit: 100

X-RateLimit-Remaining: 87

X-RateLimit-Reset: 1640000000

Retry-After: 900

\\\`

```

✅ Do This

• Use HTTPS Everywhere - Never send sensitive data over HTTP
• Implement Authentication - Require authentication for protected endpoints
• Validate All Inputs - Never trust user input
• Use Parameterized Queries - Prevent SQL injection
• Implement Rate Limiting - Protect against brute force and DDoS
• Hash Passwords - Use bcrypt with salt rounds >= 10
• Use Short-Lived Tokens - JWT access tokens should expire quickly
• Implement CORS Properly - Only allow trusted origins
• Log Security Events - Monitor for suspicious activity
• Keep Dependencies Updated - Regularly update packages
• Use Security Headers - Implement Helmet.js
• Sanitize Error Messages - Don't leak sensitive information

❌ Don't Do This

• Don't Store Passwords in Plain Text - Always hash passwords
• Don't Use Weak Secrets - Use strong, random JWT secrets
• Don't Trust User Input - Always validate and sanitize
• Don't Expose Stack Traces - Hide error details in production
• Don't Use String Concatenation for SQL - Use parameterized queries
• Don't Store Sensitive Data in JWT - JWTs are not encrypted
• Don't Ignore Security Updates - Update dependencies regularly
• Don't Use Default Credentials - Change all default passwords
• Don't Disable CORS Completely - Configure it properly instead
• Don't Log Sensitive Data - Sanitize logs

Problem: JWT Secret Exposed in Code

Symptoms: JWT secret hardcoded or committed to Git

Solution:

\\\`javascript

// ❌ Bad

const JWT_SECRET = 'my-secret-key';

// ✅ Good

const JWT_SECRET = process.env.JWT_SECRET;

if (!JWT_SECRET) {

throw new Error('JWT_SECRET environment variable is required');

}

// Generate strong secret

// node -e "console.log(require('crypto').randomBytes(64).toString('hex'))"

\\\`

Problem: Weak Password Requirements

Symptoms: Users can set weak passwords like "password123"

Solution:

\\\`javascript

const passwordSchema = z.string()

.min(12, 'Password must be at least 12 characters')

.regex(/[A-Z]/, 'Must contain uppercase letter')

.regex(/[a-z]/, 'Must contain lowercase letter')

.regex(/[0-9]/, 'Must contain number')

.regex(/[^A-Za-z0-9]/, 'Must contain special character');

// Or use a password strength library

const zxcvbn = require('zxcvbn');

const result = zxcvbn(password);

if (result.score < 3) {

return res.status(400).json({

error: 'Password too weak',

suggestions: result.feedback.suggestions

});

}

\\\`

Problem: Missing Authorization Checks

Symptoms: Users can access resources they shouldn't

Solution:

\\\`javascript

// ❌ Bad: Only checks authentication

app.delete('/api/posts/:id', authenticateToken, async (req, res) => {

await prisma.post.delete({ where: { id: req.params.id } });

res.json({ success: true });

});

// ✅ Good: Checks both authentication and authorization

app.delete('/api/posts/:id', authenticateToken, async (req, res) => {

const post = await prisma.post.findUnique({

where: { id: req.params.id }

});

if (!post) {

return res.status(404).json({ error: 'Post not found' });

}

// Check if user owns the post or is admin

if (post.userId !== req.user.userId && req.user.role !== 'admin') {

return res.status(403).json({

error: 'Not authorized to delete this post'

});

}

await prisma.post.delete({ where: { id: req.params.id } });

res.json({ success: true });

});

\\\`

Problem: Verbose Error Messages

Symptoms: Error messages reveal system details

Solution:

\\\`javascript

// ❌ Bad: Exposes database details

app.post('/api/users', async (req, res) => {

try {

const user = await prisma.user.create({ data: req.body });

res.json(user);

} catch (error) {

res.status(500).json({ error: error.message });

// Error: "Unique constraint failed on the fields: (email)"

}

});

// ✅ Good: Generic error message

app.post('/api/users', async (req, res) => {

try {

const user = await prisma.user.create({ data: req.body });

res.json(user);

} catch (error) {

console.error('User creation error:', error); // Log full error

if (error.code === 'P2002') {

return res.status(400).json({

error: 'Email already exists'

});

}

res.status(500).json({

error: 'An error occurred while creating user'

});

}

});

\\\`

Authentication & Authorization

• [ ] Implement strong authentication (JWT, OAuth 2.0)
• [ ] Use HTTPS for all endpoints
• [ ] Hash passwords with bcrypt (salt rounds >= 10)
• [ ] Implement token expiration
• [ ] Add refresh token mechanism
• [ ] Verify user authorization for each request
• [ ] Implement role-based access control (RBAC)

Input Validation

• [ ] Validate all user inputs
• [ ] Use parameterized queries or ORM
• [ ] Sanitize HTML content
• [ ] Validate file uploads
• [ ] Implement request schema validation
• [ ] Use allowlists, not blocklists

Rate Limiting & DDoS Protection

• [ ] Implement rate limiting per user/IP
• [ ] Add stricter limits for auth endpoints
• [ ] Use Redis for distributed rate limiting
• [ ] Return proper rate limit headers
• [ ] Implement request throttling

Data Protection

• [ ] Use HTTPS/TLS for all traffic
• [ ] Encrypt sensitive data at rest
• [ ] Don't store sensitive data in JWT
• [ ] Sanitize error messages
• [ ] Implement proper CORS configuration
• [ ] Use security headers (Helmet.js)

Monitoring & Logging

• [ ] Log security events
• [ ] Monitor for suspicious activity
• [ ] Set up alerts for failed auth attempts
• [ ] Track API usage patterns
• [ ] Don't log sensitive data

1. Broken Object Level Authorization - Always verify user can access resource
2. Broken Authentication - Implement strong authentication mechanisms
3. Broken Object Property Level Authorization - Validate which properties user can access
4. Unrestricted Resource Consumption - Implement rate limiting and quotas
5. Broken Function Level Authorization - Verify user role for each function
6. Unrestricted Access to Sensitive Business Flows - Protect critical workflows
7. Server Side Request Forgery (SSRF) - Validate and sanitize URLs
8. Security Misconfiguration - Use security best practices and headers
9. Improper Inventory Management - Document and secure all API endpoints
10. Unsafe Consumption of APIs - Validate data from third-party APIs

• @ethical-hacking-methodology - Security testing perspective
• @sql-injection-testing - Testing for SQL injection
• @xss-html-injection - Testing for XSS vulnerabilities
• @broken-authentication - Authentication vulnerabilities
• @backend-dev-guidelines - Backend development standards
• @systematic-debugging - Debug security issues

• [OWASP API Security Top 10](https://owasp.org/www-project-api-security/)
• [JWT Best Practices](https://tools.ietf.org/html/rfc8725)
• [Express Security Best Practices](https://expressjs.com/en/advanced/best-practice-security.html)
• [Node.js Security Checklist](https://blog.risingstack.com/node-js-security-checklist/)
• [API Security Checklist](https://github.com/shieldfy/API-Security-Checklist)

---

Pro Tip: Security is not a one-time task - regularly audit your APIs, keep dependencies updated, and stay informed about new vulnerabilities!