Which of the following is NOT a common authentication method for APIs?

Fingerprint authentication is not a common authentication method specifically used for APIs. APIs typically rely on methods that can be programmatically controlled and standardized across various platforms and services.

API keys, OAuth, and tokens are widely adopted approaches for securing API access. API keys provide a simple way to identify and authenticate clients. OAuth is a more complex framework that allows for delegated access, enabling users to grant limited access to their information without sharing credentials. Tokens, such as JSON Web Tokens (JWTs), are often used to transmit information securely between parties and can encapsulate user identity and permissions.

Fingerprint authentication, while a secure method of verifying identity, is primarily used on devices for biometric authentication and is not designed for remote API interactions, where the client and server may not be physically connected. Therefore, it does not fit within the context of standard API authentication methods.