api-security

API Security

Rules (for AI agents)

ALWAYS

• Require authentication on every non-public endpoint. Default to authenticated; opt out for genuinely public routes by explicit annotation.
• Consult auth-security for who the caller is and what they may touch. It owns the credential (algorithm pinning, expiry, lifetime, session, CSRF) and the permission (object-level BOLA/IDOR checks, multi-key routes, streaming subjects, function-level role gating). Any endpoint that reads or writes a resource by id needs it; this skill covers everything else about the endpoint.
• Validate all request inputs against an explicit schema (JSON Schema, Pydantic, Zod, validator/v10 struct tags). Reject early; never propagate untrusted input deeper.
• Enforce rate limits at the route level for authentication endpoints, password reset, and any expensive operation.
• Consult error-handling-security for what an error response may carry. It owns the boundary between what crosses to the client and what stays in the log, including presence-of-record disclosure (User not found vs Invalid credentials).
• Include Cache-Control: no-store on responses containing personal or sensitive data.

NEVER

• Use sequential integer IDs in URLs for resources accessible across tenants. Use UUIDs or unguessable opaque IDs.
• Mass-assign request bodies directly to ORM models (User(**request.json)) — this enables privilege escalation when the model has admin fields the user shouldn't control.
• Key a rate-limit / lockout counter on a client-controllable header (leftmost X-Forwarded-For, X-Real-IP, Forwarded) — rotating it yields a fresh bucket per request and defeats the limit. Derive the client IP from the trusted-proxy hop count (or key on the authenticated user), and fail closed on limiter error.
• Use HTTP GET for any state-changing operation — GET should be safe and idempotent.
• Rely on network position (IP allowlist, VPN, private subnet, "internal only", a WAF/edge rule) as the only control on a sensitive endpoint. Reachability is not authentication: the moment there's an SSRF, a compromised internal host, a tenant on the network, or a boundary change, an unauthenticated "internal" endpoint (permission_classes = [AllowAny], no RequireAuth) is wide open. Enforce auth/authz at the service itself, behind any network control.
• Place security controls (auth, field-stripping, CSRF, rate-limit, input validation) only at a gateway / BFF / proxy while the backend service is also directly reachable. An attacker calls the service directly and bypasses every proxy-layer control — controls must live at the service that owns the data. (A common variant: the gateway checks that a JWT is present but the service never checks the caller's role or object-level ownership — the service reads the subject id from the body/path/query and trusts it.)