Agent Skills: CSRF Protection

CSRF Protection

Table of Contents

• Overview
• When to Use
• Quick Start
• Reference Guides
• Best Practices

Overview

Implement comprehensive Cross-Site Request Forgery protection using synchronizer tokens, double-submit cookies, SameSite cookie attributes, and custom headers.

When to Use

• Form submissions
• State-changing operations
• Authentication systems
• Payment processing
• Account management
• Any POST/PUT/DELETE requests

Quick Start

Minimal working example:

// csrf-protection.js
const crypto = require("crypto");
const csrf = require("csurf");

class CSRFProtection {
  constructor() {
    this.tokens = new Map();
    this.tokenExpiry = 3600000; // 1 hour
  }

  /**
   * Generate CSRF token
   */
  generateToken() {
    return crypto.randomBytes(32).toString("hex");
  }

  /**
   * Create token for session
   */
  createToken(sessionId) {
    const token = this.generateToken();
    const expiry = Date.now() + this.tokenExpiry;

    this.tokens.set(sessionId, {
// ... (see reference guides for full implementation)

Reference Guides

Detailed implementations in the references/ directory:

| Guide | Contents | |---|---| | Node.js/Express CSRF Protection | Node.js/Express CSRF Protection | | Double Submit Cookie Pattern | Double Submit Cookie Pattern | | Python Flask CSRF Protection | Python Flask CSRF Protection | | Frontend CSRF Implementation | Frontend CSRF Implementation | | Origin and Referer Validation | Origin and Referer Validation |

Best Practices

✅ DO

• Use CSRF tokens for all state-changing operations
• Set SameSite=Strict on cookies
• Validate Origin/Referer headers
• Use secure, random tokens
• Implement token expiration
• Use HTTPS only
• Include tokens in AJAX requests
• Test CSRF protection

❌ DON'T

• Skip CSRF for authenticated requests
• Use GET for state changes
• Trust Origin header alone
• Reuse tokens
• Store tokens in localStorage
• Allow credentials in CORS without validation