All Google APIs (Google Calendar, Google Drive, etc.) stopped supporting OAuth1 (and by extension OAuthConfig) on April 20, 2015. OAuth is the de facto standard for authorization today and used by most modern APIs. To assist with connecting Apps Script to OAuth-protected APIs, Google recently created two new open source libraries: OAuth1 for App Scripts and OAuth2 for App Scripts. This information is fairly technical. Please see Deprecation Reminder: Migrate all Scripts away from OAuth Configuration for details.
On July 6th, 2015, Google will be shutting down the OAuthConfig class completely. This means that if users have scripts that still use OAuthConfig to connect to APIs, they must will need to update your code to use the OAuth1 for Apps Script library before July 6th, 2015.