OAuth client authentication is employed for credential protection
As a Google Docs client, GDocsDrive does not ask for your username and password to login, but OAuth 2.0 is employed for authentication and authorization.
OAuth 2.0 is a newly released authentication standard and is also the only encouraged authentication method from Google. With OAuth client login, the users login through Google’s sign in web page, and tokens are returned from Google to third party applications for further operations.
OAuth 2.0 is supported and recommended by Facebook, Google, Microsoft and lots of other online service providers. It makes it impossible for a third party app to get the user’s credentials, such as usernames and passwords.