Which of the following is NOT a method of authentication for a web API?

Token-based authentication is commonly used as a method of authentication for web APIs. It involves issuing a token after validating a user's identity, allowing for secure access to resources without sending credentials with every request.

On the other hand, basic authentication, OAuth Client Credentials Grant, and session-based authentication are all recognized methods of authentication for web APIs. Basic authentication includes sending a username and password with the request, while the OAuth Client Credentials Grant is a widely accepted protocol that allows applications to obtain a token using client credentials. Session-based authentication involves maintaining a session on the server after the user logs in, typically through the use of cookies, which also alerts the server to the user's authenticated state on subsequent requests.

In contrast, token-based authentication ensures that sensitive information is not exposed in each request, thereby enhancing security and usability across a distributed system. It is essential in modern API-driven architectures, often preferred for stateless scenarios where maintaining session state is impractical.