HasApiKey
public interface HasApiKey<O extends Api.ApiOptions>
| AuthorizationClient | A client for the authorization API. | 
| CredentialSavingClient | A client for the Credential Saving API. | 
| GoogleApi | Base class for Google API entry points. | 
| ModuleInstallClient | Interface for module install APIs. | 
| SignInClient | A client for the sign-in API. | 
| GoogleSignInClient | This class is deprecated. Use Credential Manager for authentication or Google Identity Services for authorization. | 
Anything that has an ApiKey. 
This is used to allow GoogleApi-based clients to be exposed via interface instead of subclass. Those interfaces can be declared as extending this, and GoogleApi's will automatically fulfill the interface.