Authentication is where most API integrations go wrong the first time. Not because the concepts are complicated, but because there are several distinct mechanisms in common use, they solve different problems, and developers often reach for the one they recognize rather than the one that fits. Understanding what each mechanism actually does — and what it does not do — is the difference between an integration that works and one that works until it doesn’t.

API security failures are not exotic. They rarely involve sophisticated attacks on cryptographic primitives or novel zero-day exploits. The most consequential breaches — the ones that expose millions of records, compromise user accounts, or shut down services — happen because an API allowed something it should not have, at a scale its designers did not anticipate. Understanding the fundamental attack surface of an API and designing against it deliberately is the entire discipline. It is not advanced knowledge. It is the baseline.