api-security-best-practices

API Security Best Practices

Overview

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.

When to Use This Skill

How It Works

Step 1: Authentication & Authorization

I'll help you implement secure authentication:

Step 2: Input Validation & Sanitization

Protect against injection attacks:

Step 3: Rate Limiting & Throttling

Prevent abuse and DDoS attacks:

Step 4: Data Protection

Secure sensitive data:

Step 5: API Security Testing

Verify security implementation:

Examples

Example 1: Implementing JWT Authentication

## Secure JWT Authentication Implementation

### 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

## Preventing SQL Injection and Input Validation

### 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

## Implementing Rate Limiting

### 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
\`\`\`

Best Practices

✅ Do This

❌ Don't Do This

Common Pitfalls

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'

});

}

});

\\\`

Security Checklist

Authentication & Authorization

Input Validation

Rate Limiting & DDoS Protection

Data Protection

Monitoring & Logging

OWASP API Security Top 10

Related Skills

Additional Resources

---

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