Google has been updating APIs with new versions of Drive and Calendar. The new APIs offer developers several improvements over older versions of the API. As each API is introduced, the deprecation of a set of corresponding APIs is also announced.
As of April 20, 2015, Google is discontinuing the following deprecated APIs:
Keep in mind that older protocols, such as ClientLogin, AuthSub, and OpenID 2.0, have also been deprecated and are scheduled to shut down. Be sure to switch to OAuth2 for authorization.
For more information, please see Reminder to update to Google Data APIs.