API-First Architecture Security: When APIs Are Designed Before Applications for Australian Enterprises

API-first architecture designs APIs as the primary interface before building applications — meaning API security is foundational, not an afterthought. Security testing for API-first architectures covers: API specification review (are security requirements defined in the OpenAPI spec?), contract testing (does the implementation match the specification's security requirements?), versioning strategy security, developer portal security (API key management, documentation exposure), and SDK security for client libraries distributed to API consumers.