Treat every API as a security boundary

APIs connect users, applications, AI workflows and infrastructure. Secure design makes identity, authorization, validation, failure behavior, secrets, abuse controls and audit events explicit at that boundary.

Authenticate the caller

Use an authentication mechanism appropriate to the client and environment. Do not treat possession of an endpoint URL as authentication.

Authorize every operation

Check whether the authenticated identity may perform the requested action on the specific resource, not only whether it is logged in.

Validate inputs

Validate schemas, identifiers, ranges, file types and business rules before inputs reach sensitive logic or downstream systems.

Limit abuse

Use rate limits, quotas, request-size limits and expensive-operation controls based on the real API and threat model.

Protect secrets

Keep API keys, signing keys and service credentials out of client code and logs. Scope credentials to the smallest practical capability.

Design safe errors

Return useful errors without exposing stack traces, secret values, internal paths or more system detail than the client needs.

Make retries safe

Use idempotency or duplicate protection where repeated requests could create unwanted side effects.

Log useful security events

Record authentication, authorization, administrative and high-impact events without copying unnecessary sensitive request bodies into logs.

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This guidance is defensive architecture material. It is not a penetration test, vulnerability scan, compliance assessment or claim that an API is secure.