security: add CSRF token protection (signed double-submit cookie)

[mmcintosh]

security: CSRF Token Protection

Target: SonicJs-Org/sonicjs main
Branch: security/csrf-protection

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Description

Add stateless CSRF token protection using the Signed Double-Submit Cookie pattern, providing defense-in-depth against cross-site request forgery beyond SameSite=Strict cookies alone.

This protects against same-site attacks (e.g., subdomain cookie tossing, browser bugs that bypass SameSite) with zero infrastructure overhead — no D1 tables, no KV, no session store. The token is a self-validating nonce.hmac_signature using HMAC-SHA256 keyed with the existing JWT_SECRET.

Fixes VULN-006 from the security audit.

Changes

Core Middleware

• New csrf.ts middleware (281 lines) — generates and validates CSRF tokens using HMAC-SHA256 signed double-submit cookies
• Token format: <32-byte-nonce>.<hmac_signature>, base64url-encoded, no padding
• Check-then-reuse: validates existing cookie HMAC before regenerating (reduces unnecessary Set-Cookie headers)
• Header-only validation (X-CSRF-Token) with form body fallback (_csrf hidden field) for regular HTML form POSTs
• Mounted globally in app.ts before route handlers

Exempt Paths

• Safe methods: GET, HEAD, OPTIONS
• Auth routes that create sessions: /auth/login*, /auth/register*, /auth/seed-admin, /auth/accept-invitation, /auth/reset-password
• Read-only search: /api/search*
• Public form submissions: /forms/*, /api/forms/* (NOT /admin/forms/*)
• Bearer-only or API-key-only requests (no auth_token cookie present)

Auth Integration

• auth.ts: Set csrf_token cookie on login/register (all 7 handlers), clear on logout
• Cookie attributes: HttpOnly, SameSite=Strict, Secure (production), Path=/

Admin Layout

• Global CSRF script in admin-layout-catalyst.template.ts:
  • getCsrfToken() reads csrf_token from cookie (handles = in base64 values)
  • htmx:configRequest listener auto-attaches X-CSRF-Token header to all HTMX requests
  • fetch() wrapper auto-attaches header to all non-GET fetch calls
  • submit event listener injects hidden _csrf field into regular (non-HTMX) form submissions

Form Templates

• Hidden _csrf input field added to form.template.ts and components/form.template.ts as defense-in-depth

Error Responses

• Browser requests (Accept: text/html): HTML 403 page with "CSRF token missing or invalid"
• API requests: JSON { error: "CSRF token missing", status: 403 }
• Production warning logged when JWT_SECRET is not set

Technical Details

New Files:

File	Lines	Description
packages/core/src/middleware/csrf.ts	281	CSRF middleware implementation
packages/core/src/__tests__/middleware/csrf.test.ts	525	Unit tests (40 tests)

Modified Files:

File	Description
packages/core/src/middleware/index.ts	Export csrf middleware
packages/core/src/app.ts	Mount csrf middleware globally
packages/core/src/routes/auth.ts	Set/clear csrf_token on login/register/logout
packages/core/src/templates/layouts/admin-layout-catalyst.template.ts	CSRF auto-attach script
packages/core/src/templates/form.template.ts	Hidden _csrf field
packages/core/src/templates/components/form.template.ts	Hidden _csrf field
tests/e2e/utils/test-helpers.ts	CSRF helper functions for E2E tests
tests/e2e/02b-authentication-api.spec.ts	Add CSRF headers to auth API tests
tests/e2e/08b-admin-collections-api.spec.ts	Add CSRF headers to collections API tests
tests/e2e/13-migrations.spec.ts	Add CSRF headers to migrations API tests
tests/e2e/14-database-tools.spec.ts	Add CSRF headers to database tools API tests
tests/e2e/23-content-api-crud.spec.ts	Add CSRF headers to content CRUD API tests

Testing

Unit Tests

• 40 unit tests added (csrf.test.ts)
• All unit tests passing

Unit test coverage:

• Token generation: format, uniqueness (2 tests)
• Token validation: valid, wrong secret, tampered nonce, tampered signature, empty, no dot, null/undefined (6 tests)
• Base64url encoding: URL-safe, no padding (1 test)
• Safe methods: GET, HEAD, OPTIONS pass through, cookie set on GET (3 tests)
• Cookie reuse: skip regeneration for valid, regenerate for invalid (2 tests)
• State-changing requests: valid POST/PUT/DELETE/PATCH, reject missing cookie, missing header, mismatched tokens, invalid signature (8 tests)
• Exempt paths: all 8 auth routes, /forms/*, /api/forms/*, NOT /admin/forms/*, custom paths (9 tests)
• Bearer/API-key exemption: no cookie = no CSRF required (2 tests)
• Error responses: HTML for browsers, JSON for API (2 tests)
• JWT_SECRET warning: production warning, no warning in dev (2 tests)

E2E Tests

• 6 existing E2E test files updated for CSRF compatibility
• All E2E tests passing (676+ tests across 3 CI shards)

Performance Impact

Metric	Impact	Notes
Latency per request	~0.1ms	Single HMAC-SHA256 verify per state-changing request
Memory	Negligible	No session store, no D1/KV queries
Cookie overhead	~120 bytes	One additional cookie (csrf_token)
GET requests	No validation	Only ensures cookie exists

Breaking Changes

Potentially breaking for custom integrations:

• Any client making POST/PUT/DELETE/PATCH requests with cookie-based auth (auth_token cookie) must now include the X-CSRF-Token header matching the csrf_token cookie value
• Bearer-only and API-key-only requests are NOT affected
• Public form submissions (/forms/*, /api/forms/*) are NOT affected

Migration for API consumers using cookie auth:

// Read csrf_token from cookie
const csrfToken = document.cookie.match(/csrf_token=([^;\s]+)/)?.[1] || '';

// Include in state-changing requests
fetch('/admin/api/content', {
  method: 'POST',
  headers: {
    'X-CSRF-Token': csrfToken,
    'Content-Type': 'application/json'
  },
  body: JSON.stringify(data)
});

Migration Notes

• No database migrations required
• No configuration changes required — uses existing JWT_SECRET binding
• CSRF protection activates automatically on deployment
• Existing admin UI (HTMX-based) automatically includes tokens via the global script
• Custom frontends using cookie auth will need to add the X-CSRF-Token header

Known Issues

None.

Screenshots/Videos

N/A (middleware-only change, no UI changes)

Checklist

• Code follows project conventions
• Tests added/updated and passing (40 unit + 676+ E2E)
• Type checking passes
• No console errors or warnings
• Documentation updated (inline JSDoc + code comments)
• No breaking changes for default usage (admin UI auto-handles tokens)
• Backward compatible for Bearer/API-key auth consumers