csrf

Provides CSRF protection using HMAC-signed tokens. Unlike other middleware, csrf() returns an object with two methods — issue and verify — rather than a single middleware function. In ergo-router, the pipeline builder automatically dispatches issue for safe methods (GET, HEAD, OPTIONS) and verify for unsafe methods.

Pipeline stage: Authorization

Bearer token APIs do not need CSRF

CSRF protection is only necessary when the browser automatically attaches credentials (cookies). APIs that authenticate exclusively via Authorization: Bearer headers are not vulnerable to CSRF.

Import

import {csrf} from '@centralping/ergo';

Options

Option	Type	Default	Description
secret	string	—	Required. HMAC secret for token signing
cookieTokenName	string	'CSRF-TOKEN'	Cookie name for the CSRF token
headerTokenName	string	'X-CSRF-TOKEN'	Request header name for the token
cookieUuidName	string	'CSRF-UUID'	Cookie name for the CSRF UUID
encoding	string	'base64'	Token encoding
cookieOptions	object	{}	Cookie directives (note: httpOnly and sameSite are locked)

Cookie middleware is required

Both issue and verify read from the domain accumulator at acc.cookies — the cookie jar populated by the cookie middleware. Cookie middleware must run before CSRF in the pipeline. In ergo-router, set cookie: true (or a cookie options object) in defaults or per-route config alongside csrf. In standalone compose(), place cookie() before the CSRF middleware in the pipeline array.

Cookie Security

• Token cookie: httpOnly: false (locked — client JS must read it), sameSite: 'Strict' (locked)
• UUID cookie: httpOnly: true (locked — set after cookieOptions spread), sameSite: 'Strict' (locked)
• sameSite cannot be overridden via cookieOptions on either cookie
• Token cookie httpOnly: false and UUID cookie httpOnly: true cannot be overridden (set after cookieOptions spread)

Return Value

The factory returns {issue, verify}:

• issue(req, res, acc) — Sets token and UUID cookies on the jar (acc.cookies). No return value.
• verify(req, res, acc) — Compares the request header token against the cookie using crypto.timingSafeEqual(). Returns undefined on success. On failure, returns {response: {statusCode: 403, detail: 'CSRF verification failed'}}.

ergo-router Stage 2 ordering

In ergo-router’s pipeline builder, CSRF verification runs before authorization in Stage 2 (Authorization). This ensures the request’s integrity is verified before credential checks on unsafe methods.

Error Responses

Status	Condition
403 Forbidden	Missing header token, missing UUID cookie, or token verification fails

Usage

When CSRF Applies

CSRF attacks exploit a browser behavior: cookies are automatically attached to every request to the cookie’s origin, regardless of which site initiated the request. A malicious page can submit a form or fire a fetch to your API and the browser will include the user’s session cookie — without the user’s knowledge. CSRF tokens prevent this by requiring a secondary proof of intent that the attacking site cannot access.

This means CSRF protection is tied to your authentication mechanism, not your API’s functionality:

Auth mechanism	Client type	CSRF needed?	Rationale
Session cookie	Browser	Yes	Browsers auto-attach cookies — CSRF prevents forged submissions
Bearer token	Mobile/service	No	Tokens are explicitly attached by the client — not auto-sent by the browser
Cookie + Bearer (mixed)	Both	Per-route	Enable CSRF on cookie-auth routes, disable on Bearer-only routes
None (public)	Any	No	No credentials to protect

For APIs that serve both browser and token-based clients, configure CSRF per-route — enable it on cookie-authenticated routes and disable it on Bearer-only routes with csrf: false. See Mixed-Auth CORS & CSRF for the complete implementation pattern.

For configuring authentication strategies (Bearer, Basic, API key), see the authorization middleware guide.

Standalone

import {compose, cookie, csrf} from '@centralping/ergo';

const csrfMiddleware = csrf({secret: process.env.CSRF_SECRET});

// Issue tokens on GET
const issuePipeline = compose(
  cookie(),
  {fn: csrfMiddleware.issue, setPath: 'csrf'},
);

// Verify tokens on POST
const verifyPipeline = compose(
  cookie(),
  {fn: csrfMiddleware.verify, setPath: 'csrf'},
);

ergo-router

import createRouter from '@centralping/ergo-router';

const router = createRouter({
  defaults: {
    cookie: true,
    csrf: {secret: process.env.CSRF_SECRET},
  },
});

// Browser route — inherits cookie + CSRF from defaults.
// GET/HEAD/OPTIONS → issue (sets token cookies)
// POST/PUT/PATCH/DELETE → verify (checks X-CSRF-TOKEN header)
router.get('/account/settings', {
  execute: (req, res, acc) => ({
    response: {body: {settings: {theme: 'dark'}}},
  }),
});

router.post('/account/settings', {
  execute: async (req, res, acc) => ({
    response: {body: {updated: true}},
  }),
});

// Bearer-only route — disables CSRF (token clients are not
// vulnerable). cookie: false is optional since cookie middleware
// has no effect without CSRF, but makes intent explicit.
router.post('/api/webhooks', {
  csrf: false,
  cookie: false,
  execute: async (req, res, acc) => ({
    response: {body: {received: true}},
  }),
});

cookie: true is required alongside csrf — cookie middleware populates acc.cookies, which both issue and verify depend on. See Config Resolution for how defaults, true, false, and per-route overrides interact.

RFC References

• OWASP CSRF Prevention Cheat Sheet

Related Recipes

• Mixed-Auth CORS & CSRF — Configuring CORS and CSRF together for browser and token-based clients
• Secure Mutations — Integrated CSRF + auth + idempotency workflow with client-side fetch wiring

API Reference

See the auto-generated csrf API docs.