The Complete Production SOP: How to Deploy and Run CSRF Prevention with Double-Submit & SameSite Cookies in Autonomous AI Agents
Production SOP to install and run csrf-token-samesite-cookies in Codex, Claude Code, Cursor, and Windsurf. Includes double-submit HMAC and SameSite rules.
Technical Overview & Architectural Context
Autonomous coding agents frequently introduce subtle yet critical vulnerabilities when scaffolding authentication layers, API route handlers, and session state management. Large language models commonly default to obsolete patterns—such as relying solely on Authorization headers for browser-based Single Page Applications (SPAs) or setting cookie configurations with missing `SameSite`, `HttpOnly`, or `Secure` flags. Left unguided, agents often generate naive double-submit cookie schemes susceptible to subdomain collision, timing attacks, or unverified top-level navigations. The `csrf-token-samesite-cookies` skill resolves this by establishing rigid, deterministic Standard Operating Procedures (SOPs) within the agent's execution context. It forces the agent to implement cryptographically secure, signed HMAC double-submit cookies or stateful session tokens, verify `Origin` and `Sec-Fetch-Site` request headers, and enforce strict cookie attributes (`SameSite=Lax` or `SameSite=Strict`). Furthermore, the skill sets strict file modification boundaries, preventing autonomous agents from introducing insecure fallback bypasses.
Prerequisites & Environment Requirements
Verified Search Intents & Long-Tail Queries Solved
This operational tutorial is engineered to provide deterministic solutions for these developer search queries:
Step-by-Step Execution Playbook
Local Environment Setup & SKILL.md Mounting
Create the local skill manifest directory and inject verified procedural rules into agent runtime contexts.
Autonomous runtimes such as Claude Code, Cursor, and Windsurf inspect predefined rule directories (`.agents/skills`, `.cursor/rules`, or `.windsurfrules`). Mounting `csrf-token-samesite-cookies` directly into the agent workspace registers the frontmatter metadata triggers so the agent invokes CSRF safeguards automatically when generating mutation routes.
mkdir -p .agents/skills/csrf-token-samesite-cookies && curl -fsSL https://askills.dev/api/skills/csrf-token-samesite-cookies/raw -o .agents/skills/csrf-token-samesite-cookies/SKILL.md---
name: "csrf-token-samesite-cookies"
description: "Prevent Cross-Site Request Forgery with SameSite cookies and cryptographically secure tokens."
metadata:
author: "OWASP"
version: "1.0.0"
runtime_compatibility:
- "codex"
- "claude-code"
- "cursor"
- "windsurf"
triggers:
- "prevent csrf attack"
- "configure samesite cookies"
- "implement csrf token middleware"
permissions:
fs_read: true
fs_write: "workspace"
shell_exec: false
net_access: false
---Place the SKILL.md in project-level `.agents/skills` rather than global user directories to minimize agent context pollution when switching between non-web repositories.
Ensure `fs_write` is constrained to `workspace`. Granting agents global write permissions can lead to unauthorized modifications of system-level TLS or reverse proxy configs.
Environment Secrets & Dependency Validation
Configure cryptographic secret keys and cookie signing salts without committing secrets to version control.
HMAC-based double-submit CSRF tokens require an application secret to prevent token forgery by malicious actors who control a sibling subdomain. The agent must verify that `CSRF_SECRET` is declared in local environment templates before implementing the middleware.
test -f .env.local || cp .env.example .env.local && echo 'CSRF_SECRET='$(openssl rand -hex 32) >> .env.localInstruct the agent to look for `process.env.CSRF_SECRET` or `os.environ['CSRF_SECRET']` dynamically rather than hardcoding static fallback salts into middleware files.
Verify `.env.local` is included in `.gitignore`. Runtimes like Claude Code might stage generated test environment files if not explicitly excluded.
Intent Matching & Trigger Invocation
Execute the task using natural language prompts aligned with frontmatter triggers.
When prompted with triggers like 'implement csrf token middleware', the runtime matches the skill manifest. The agent reads the procedural SOP, enforcing strict HTTP cookie flags (`SameSite=Lax`, `HttpOnly`, `Secure`) and constant-time token comparisons (`crypto.timingSafeEqual`) for all state-changing verbs.
Explicitly mention HTTP methods (POST, PUT, DELETE, PATCH) in your prompt to force the agent to skip idempotent GET/HEAD routes safely.
Do not instruct the agent to disable CSRF verification in development environments without restricting the bypass strictly to automated headless testing flags.
Verification, Linting & Output Quality Gate
Execute automated self-healing checks and run test suites before accepting agent deliverables.
The skill mandates that the agent verify its own implementation using local test runners and linter suites. The agent executes test cases covering missing tokens, token mismatches, origin mismatches, and valid submissions, asserting a clean return code 0.
npm test -- tests/csrf.test.ts || pytest tests/test_csrf.pyInstruct the agent to inspect the git diff against the master branch before concluding the turn to ensure no unwanted files were altered.
If using Jest or Vitest with cookie-parser, ensure cookie signing mocks provide valid hexadecimal secrets; otherwise, tests fail silently on falsy token comparisons.
Real-World Scenario: Hardening Express/TypeScript API Endpoints Against CSRF Using Signed Double-Submit Cookies
“Implement csrf token middleware for our Express TypeScript application. Configure samesite cookies for sessions and prevent csrf attacks on all mutation endpoints.”
Runtime Troubleshooting & Failure Modes
Root Cause: The client application sent an asynchronous request without attaching the custom `X-CSRF-Token` header, or the `SameSite` attribute was set to `Strict` causing cookie stripping during navigation transitions from trusted third-party OAuth redirect flows.
// Ensure middleware inspects both custom header and body fallback:
const clientToken = req.headers['x-csrf-token'] || req.body?._csrf;
if (!clientToken || !verifyHmacToken(clientToken, req.cookies['__Host-csrf-token'])) {
return res.status(403).json({ error: 'CSRF token validation failed' });
}Root Cause: The agent implemented a raw string equality comparison or invoked `crypto.timingSafeEqual` with mismatched Buffer byte lengths between the request token and the expected HMAC hash.
function safeCompare(a: string, b: string): boolean {
const bufA = Buffer.from(a);
const bufB = Buffer.from(b);
return bufA.length === bufB.length && crypto.timingSafeEqual(bufA, bufB);
}Frequently Asked Questions (CSRF Prevention with Double-Submit & SameSite Cookies SOP)
Q:Can I use CSRF Prevention with Double-Submit & SameSite Cookies across Codex, Claude Code, and Cursor simultaneously?
Yes. The skill conforms to the universal SKILL.md specification. Runtimes including Codex, Claude Code, Cursor, and Windsurf read the declarative YAML metadata and trigger definitions identically.
Q:How does CSRF Prevention with Double-Submit & SameSite Cookies prevent context window overflow during long agent sessions?
The skill provides a compact, rule-bound execution checklist rather than sprawling boilerplate. By constraining instructions to key boundary conditions (HMAC validation, cookie flags, and HTTP verb filtering), agent context usage remains lean and token-efficient.
Q:Does this skill require escalated root or container permissions?
No. The skill possesses an audited security score of 98/100. It requires only standard workspace file-read and file-write permissions, with no shell execution or outbound network access required.
Ready to equip your autonomous agent with CSRF Prevention with Double-Submit & SameSite Cookies?
Copy the complete audited SKILL.md specification or download the 1-click zip bundle directly from our verified registry.