API Security

API security encompasses the authentication, authorization, input validation, rate limiting, and monitoring controls applied to APIs to ensure only legitimate clients can invoke endpoints, only within their permitted scope, and only at acceptable volumes. As APIs have become the primary integration mechanism for web and cloud services, they have also become a primary attack surface: the OWASP API Security Top 10 documents the most common API-specific vulnerability classes.

APIs frequently expose sensitive data and business logic more directly than traditional web interfaces. A broken authentication control on an API endpoint can expose every user's data. An authorization flaw — accessing another user's resources by manipulating an ID parameter — is trivially exploitable at scale. Absent rate limiting, APIs are vulnerable to credential stuffing, enumeration, and denial-of-service. Because API traffic often bypasses perimeter controls designed for browser-based requests, dedicated API security controls are necessary.

Effective API security starts with strong authentication — API keys, OAuth 2.0 tokens, or mTLS — so that every request is tied to a known caller. Authorization is enforced at the endpoint level using scoped permissions so callers can only access resources they are entitled to. Input validation rejects malformed or oversized payloads. Rate limiting caps request volume per client to prevent abuse. Audit logging records all API calls with caller identity, timestamp, and outcome, providing an immutable trail for incident investigation.