API Security Hardening

API Security Hardening

Category: Security Time Saved: Hours of security review, prevents incidents Battle-tested: Yes — AIRS Enterprise, HeadstartWebsite, GCX_Master

The Problem

You're building an HTTP API. It works, but you haven't implemented security layers. One breach, one cost attack, one data leak — and you're explaining to leadership why the API was exposed.

The Four Layers

Every production API needs these four defenses. Missing any one creates an exploitable gap.

1. Rate Limiting

Prevent abuse and cost attacks.

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

const limiter = rateLimit({
  windowMs: 60 * 1000,  // 1 minute
  max: 100,             // 100 requests per window per IP
  standardHeaders: true,
  legacyHeaders: false,
  message: { error: 'Too many requests, slow down' }
});

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

Rules:

• Use sliding window, not fixed window (prevents burst at window boundaries)
• Per-user limits (100/min) AND per-IP limits (1000/min)
• For serverless: Upstash Redis (@upstash/ratelimit)

2. JWT Validation

Never trust tokens without verification.

const jwt = require('jsonwebtoken');

function validateToken(token) {
  return jwt.verify(token, publicKey, {
    algorithms: ['RS256'],  // Explicit allowlist — NEVER omit
    issuer: 'https://your-auth-server.com',
    audience: 'your-api-identifier',
  });
}

Rules:

• Validate issuer, audience, expiration, AND signature
• Explicit algorithm allowlist (algorithms: ['RS256']) — prevents algorithm confusion attacks
• Never decode without verification (jwt.decode is NOT validation)

3. CORS Configuration

Block cross-origin abuse.

const cors = require('cors');

const corsOptions = {
  origin: [
    'https://your-app.com',
    'https://staging.your-app.com'
  ],
  methods: ['GET', 'POST', 'PUT', 'DELETE'],
  allowedHeaders: ['Content-Type', 'Authorization'],
  maxAge: 86400  // Preflight cache: 24 hours
};

app.use(cors(corsOptions));

Rules:

• Never use origin: '*' in production
• Explicit origin allowlist
• Include Access-Control-Max-Age for preflight caching
• For credentialed requests: credentials: true (but then NO wildcards anywhere)

4. Input Validation

Reject bad data at the boundary.

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

const CreateUserSchema = z.object({
  email: z.string().email(),
  name: z.string().min(1).max(100),
  age: z.number().int().min(0).max(150).optional(),
});

app.post('/users', (req, res) => {
  const result = CreateUserSchema.safeParse(req.body);
  if (!result.success) {
    return res.status(400).json({ errors: result.error.issues });
  }
  // result.data is now typed and validated
  createUser(result.data);
});

Rules:

• Validate at the boundary — don't let bad data propagate
• Use Zod, Joi, or similar for request body, query params, AND path params
• Reject early with clear error messages (but don't leak internals)

Checklist

Anonymous Endpoint Warning

Serverless APIs with anonymous POST endpoints (image generation, AI inference) need extra protection:

• IP-based rate limiting (even without auth)
• Request size limits (express.json({ limit: '1mb' }))
• Async processing with queue (don't hold HTTP connection during expensive ops)
• Budget alerts at 50%, 80%, 100% of monthly allocation

Source: Promoted from AI-Memory global-knowledge.md (2026-04-27)