Which authentication method utilizes service accounts?

The correct answer highlights that both API Key and OAuth Client Credentials Grant can effectively utilize service accounts.

Service accounts are non-human accounts created specifically for automated tasks and machine-to-machine communication. They are often used in environments where applications need to authenticate without user intervention, which is where the importance of API Key and OAuth Client Credentials Grant comes into play.

API Keys are often tied to a service account that is assigned permissions to access specific resources programmatically. This allows applications to communicate securely without needing a user to log in. When the application makes a request, it sends the API Key alongside the request to authenticate itself.

On the other hand, the OAuth Client Credentials Grant is specifically designed for scenarios involving service accounts. In this grant flow, a service sends its credentials to the authorization server to obtain an access token. This token is then used to authenticate and authorize requests made by the service account to access the protected resources.

In summary, both API Key and OAuth Client Credentials Grant are capable of leveraging service accounts effectively, making the combined choice the correct response.