Developers of applications that require end-user authenticated interaction with Google services now have several options for authenticating:
  • Installed Applications: "The ClientLogin API lets you incorporate programmatic login into your desktop or mobile applications. This API incorporates CAPTCHA for greater security against password trollers."
  • Proxy for Web Applications: "The AuthSub API gives your web application the ability to access a user's Google services accounts without handling the user's login information. This API offers a secure mode, in which the web application can register with Google for greater security."
The Auth Overview page has further details.