What is API authentication? + 6 authentication methods

In modern web applications, API authentication is crucial for ensuring secure interactions with internal and third-party services, protecting sensitive data, and complying with regulatory frameworks like GDPR and PCI DSS. Authentication verifies the identity of a client making API requests, using credentials such as API keys, JWTs, OAuth tokens, or mutual TLS certificates, and should not be confused with authorization, which determines access permissions. Each authentication method offers different trade-offs in terms of security, usability, and implementation complexity, with considerations like statelessness, ease of credential rotation, and expiration rules playing vital roles. Proper authentication not only safeguards against unauthorized access and attacks like credential stuffing and session hijacking but also supports operational reliability through rate limiting and access logging, which are essential for compliance audits and debugging. Webflow, for instance, uses personal access tokens for its CMS API to ensure secure integration in CI/CD workflows. Various authentication mechanisms, such as API keys, JWTs, OAuth 2.0, and mutual TLS, can be combined to address specific security challenges, each offering distinct advantages and limitations based on the context in which they are deployed.