{
  "id": "ai-rules-for-auth-and-security",
  "type": "rules",
  "category": "rules",
  "locale": "es",
  "url": "/es/rules/ai-rules-for-auth-and-security",
  "title": "Reglas de Codificación de IA para Autenticación y Seguridad",
  "description": "Reglas de AGENTS.md para autenticación y seguridad que evitan que los agentes implementen criptografía personalizada, filtren secretos o omitan verificaciones de autorización.",
  "tools": [
    "Cursor",
    "Claude Code",
    "Codex",
    "Windsurf"
  ],
  "stack": [
    "Next.js",
    "TypeScript",
    "PostgreSQL"
  ],
  "tags": [
    "agents-md",
    "auth",
    "security",
    "typescript",
    "conventions"
  ],
  "difficulty": null,
  "updated": "2026-06-08",
  "markdown": "Coloca esto en la raíz de tu repositorio como `AGENTS.md`. Las reglas de seguridad deben ser `strict` — los agentes son altamente capaces de escribir código que es funcionalmente correcto pero introduce vulnerabilidades críticas de autenticación o autorización.\n\n## AGENTS.md\n\n```md title=\"AGENTS.md\"\n# Project Rules — Auth and Security\n\n## Authentication — hard rules\n- NEVER implement custom password hashing. Use `bcrypt`, `argon2`, or the auth\n  library's built-in hashing (Better Auth, Auth.js, Clerk, Supabase Auth). Custom\n  hashing is almost always wrong and may be cryptographically broken.\n- NEVER store plaintext passwords, plaintext tokens, or plaintext secrets in the\n  database. Hash passwords; hash or encrypt tokens before persistence.\n- NEVER roll custom JWT signing or verification. Use a well-audited library\n  (`jose`, `jsonwebtoken`). Never use `alg: \"none\"` — reject tokens with no algorithm.\n- Session tokens must be at least 128 bits of cryptographic randomness. Use\n  `crypto.getRandomValues()` (Web) or `crypto.randomBytes(32)` (Node.js).\n  Do NOT use `Math.random()` for any security-relevant value.\n- NEVER store session tokens or JWTs in `localStorage`. Use `HttpOnly`, `Secure`,\n  `SameSite=Lax` cookies. `localStorage` is readable by any XSS payload on the page.\n\n## Authorization — hard rules\n- Every API route and server action MUST check the current user's session before\n  accessing data. Do not assume that reaching a route implies authorization.\n- Authorization checks must verify ownership or role, not just authentication.\n  \"Is logged in\" is authentication. \"Is allowed to read this resource\" is authorization.\n  Both are required.\n- Never pass a user-controlled ID directly into a database query without first\n  verifying that the authenticated user has permission to access that record.\n  This is an IDOR (Insecure Direct Object Reference) vulnerability.\n- In Next.js App Router: run auth checks in middleware OR at the top of every\n  Server Component and Server Action that touches user data. Do not rely on\n  client-side redirects for access control.\n\n## Secrets management\n- All secrets (API keys, database URLs, OAuth client secrets) live in environment\n  variables. Validate them with Zod at startup via `src/lib/env.ts`.\n- NEVER commit secrets to the repository. If a secret is accidentally committed,\n  treat it as compromised immediately — rotate it before doing anything else.\n- NEVER log secrets, tokens, or full request bodies that may contain credentials.\n  Scrub sensitive fields before logging.\n- Client-side code must never contain secrets. In Next.js, only variables prefixed\n  with `NEXT_PUBLIC_` are exposed to the client — and only non-sensitive values\n  should use that prefix.\n\n## Input validation and output encoding\n- Validate all user input at the server boundary with Zod before use. Never trust\n  client-provided data, including data in headers, cookies, or URL parameters.\n- Sanitize any HTML rendered from user input. Use a library (`DOMPurify`, `sanitize-html`)\n  — do NOT write a custom HTML sanitizer.\n- When constructing URLs from user input, use the `URL` constructor to parse and\n  validate. Never concatenate user input into a URL string that will be fetched\n  server-side — this is an SSRF vector.\n\n## CSRF and clickjacking\n- All state-mutating endpoints (POST, PUT, PATCH, DELETE) must be protected against\n  CSRF. In Next.js App Router, Server Actions are CSRF-protected by default; do not\n  disable this. For custom API routes, verify the `Origin` header or use a CSRF token.\n- Add `X-Frame-Options: DENY` or `Content-Security-Policy: frame-ancestors 'none'`\n  to pages that should not be embedded in iframes.\n\n## Definition of done\n- No `Math.random()` calls in authentication or token generation paths.\n- No `localStorage` for session/token storage (grep the codebase).\n- Every API route handler has an auth check at the top.\n- `NEXT_PUBLIC_` env vars contain no secrets (audit the list before shipping).\n- Zod validation runs on all form inputs before they touch the database.\n```\n\n## Por qué estas reglas\n\n- **No usar `localStorage` para tokens** elimina el error de seguridad más extendido en aplicaciones React/Next.js. Los agentes que copian patrones de autenticación de tutoriales antiguos (anteriores a 2020) frecuentemente almacenan JWTs en `localStorage`, que es trivialmente legible por cualquier script de terceros en la página. Las cookies `HttpOnly` no son accesibles desde JavaScript en absoluto — son el mecanismo de almacenamiento correcto.\n- **Las verificaciones de autorización confirman propiedad, no solo autenticación** cierra la vulnerabilidad IDOR que los agentes omiten con mayor frecuencia. Un agente al que se le pide \"agregar un endpoint para obtener el pedido de un usuario\" típicamente verifica `if (!session)` pero no `if (order.userId !== session.user.id)` — porque la segunda verificación requiere entender la semántica de propiedad del modelo de datos, que es específica del proyecto y no está implícita en la descripción de la tarea.\n\n## Buen ajuste\n\n- Cualquier aplicación con cuentas de usuario, recursos protegidos o datos de pago — esencialmente cualquier aplicación web de producción.\n\n## No es adecuado\n\n- Herramientas internas detrás de una VPN corporativa o control de acceso a nivel de red, donde el modelo de amenazas es diferente y algunos de estos controles pueden ser manejados por la capa de infraestructura."
}