cloudflare-workers-security

secondsky/claude-skillsSecurityReview advisedSnapshot d7e551aedffe

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Summary

Cloudflare Workers security with authentication, CORS, rate limiting, input validation. Use for securing APIs, JWT/API keys, or encountering auth failures, CORS errors, XSS/injection vulnerabilities.

SKILL.md

Cloudflare Workers Security

Comprehensive security patterns for protecting Workers and APIs.

Quick Security Checklist

// 1. Validate all input
const validated = schema.parse(await request.json());

// 2. Authenticate requests
const user = await verifyToken(request.headers.get('Authorization'));
if (!user) return new Response('Unauthorized', { status: 401 });

// 3. Rate limit
const limited = await rateLimiter.check(clientIP);
if (!limited.allowed) return new Response('Too Many Requests', { status: 429 });

// 4. Add security headers
response.headers.set('X-Content-Type-Options', 'nosniff');
response.headers.set('X-Frame-Options', 'DENY');

// 5. Use HTTPS-only cookies
headers.set('Set-Cookie', 'session=xxx; Secure; HttpOnly; SameSite=Strict');

Critical Rules

Never trust client input - Validate and sanitize everything
Use secure secrets - Store in Wrangler secrets, never in code
Implement rate limiting - Protect against abuse
Set security headers - Prevent common attacks
Use CORS properly - Don't use * in production

Top 10 Security Errors

Vulnerability	Symptom	Prevention
Missing auth	Unauthorized access	Verify tokens on every request
SQL injection	Data breach	Use parameterized queries with D1
XSS	Script injection	Sanitize output, set CSP
CORS misconfiguration	Blocked requests or open access	Configure specific origins
Secrets in code

async function verifyJWT(token: string, secret: string): Promise<{ valid: boolean; payload?: unknown }> {
  try {
    const [headerB64, payloadB64, signatureB64] = token.split('.');

    // Verify signature
    const key = await crypto.subtle.importKey(
      'raw',
      new TextEncoder().encode(secret),
      { name: 'HMAC', hash: 'SHA-256' },
      false,
      ['verify']
    );

    const signature = Uint8Array.from(atob(signatureB64.replace(/-/g, '+').replace(/_/g, '/')), c => c.charCodeAt(0));
    const data = new TextEncoder().encode(`${headerB64}.${payloadB64}`);

    const valid = await crypto.subtle.verify('HMAC', key, signature, data);
    if (!valid) return { valid: false };

    // Decode payload
    const payload = JSON.parse(atob(payloadB64.replace(/-/g, '+').replace(/_/g, '/')));

    // Check expiration
    if (payload.exp && Date.now() / 1000 > payload.exp) {
      return { valid: false };
    }

    return { valid: true, payload };
  } catch {
    return { valid: false };
  }
}

async function validateApiKey(
  request: Request,
  env: Env
): Promise<{ valid: boolean; clientId?: string }> {
  const apiKey = request.headers.get('X-API-Key');
  if (!apiKey) return { valid: false };

  // Hash the key for lookup (never store plain keys)
  const keyHash = await sha256(apiKey);

  // Lookup in KV or D1
  const client = await env.KV.get(`apikey:${keyHash}`, 'json');
  if (!client) return { valid: false };

  return { valid: true, clientId: client.id };
}

async function sha256(str: string): Promise<string> {
  const buffer = await crypto.subtle.digest('SHA-256', new TextEncoder().encode(str));
  return [...new Uint8Array(buffer)].map(b => b.toString(16).padStart(2, '0')).join('');
}

import { z } from 'zod';

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

async function handleCreate(request: Request): Promise<Response> {
  try {
    const body = await request.json();
    const user = UserSchema.parse(body);

    // Safe to use validated data
    return Response.json({ success: true, user });
  } catch (error) {
    if (error instanceof z.ZodError) {
      return Response.json({ error: 'Validation failed', details: error.errors }, { status: 400 });
    }
    throw error;
  }
}

function addSecurityHeaders(response: Response): Response {
  const headers = new Headers(response.headers);

  // Prevent MIME type sniffing
  headers.set('X-Content-Type-Options', 'nosniff');

  // Prevent clickjacking
  headers.set('X-Frame-Options', 'DENY');

  // XSS protection
  headers.set('X-XSS-Protection', '1; mode=block');

  // Content Security Policy
  headers.set('Content-Security-Policy', "default-src 'self'; script-src 'self'");

  // HSTS
  headers.set('Strict-Transport-Security', 'max-age=31536000; includeSubDomains');

  // Referrer policy
  headers.set('Referrer-Policy', 'strict-origin-when-cross-origin');

  return new Response(response.body, { status: response.status, headers });
}

const ALLOWED_ORIGINS = ['https://app.example.com', 'https://admin.example.com'];

function handleCORS(request: Request, response: Response): Response {
  const origin = request.headers.get('Origin');

  if (!origin || !ALLOWED_ORIGINS.includes(origin)) {
    return response; // No CORS headers
  }

  const headers = new Headers(response.headers);
  headers.set('Access-Control-Allow-Origin', origin);
  headers.set('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, OPTIONS');
  headers.set('Access-Control-Allow-Headers', 'Content-Type, Authorization');
  headers.set('Access-Control-Allow-Credentials', 'true');
  headers.set('Access-Control-Max-Age', '86400');

  return new Response(response.body, { status: response.status, headers });
}

Template	Purpose	Use When
`templates/auth-middleware.ts`	JWT/API key auth	Adding authentication
`templates/cors-handler.ts`	CORS middleware	Handling cross-origin
`templates/rate-limiter.ts`	Rate limiting	Preventing abuse
`templates/secure-worker.ts`	Full secure setup	Starting secure project

cloudflare-workers-security

Summary

SKILL.md

Cloudflare Workers Security

Quick Security Checklist

Critical Rules

Top 10 Security Errors

Authentication Patterns

JWT Verification

API Key Validation

Input Validation

With Zod

Security Headers

CORS Configuration

When to Load References

Templates

Scripts

Resources

Related skills