How do I start?
Right now, there are two libraries available for the Authentication service. Choose the one that suits your needs:
Authentication for Installed Applications: The ClientLogin API lets you incorporate programmatic login into your desktop or mobile applications. This API supports CAPTCHA for greater security against password trollers.
Authentication for Web Applications: The AuthSub API lets your web application access a user's Google data without handling the user's login information. This API offers a standard mode and a secure mode, in which the web application can register with Google for greater security.
* CAPTCHA is a trademark of Carnegie Mellon University
What is the Account Authentication Service?
At Google, we welcome the development of third-party applications that rely on and communicate with Google services. Many of these services require users to log into their Google Accounts, which means your application needs some way to manage user authentication. The Google Accounts Authentication Service helps streamline this task by validating requests for access and issuing authentication tokens. Many Google services support the Authentication Service, including those based on the Google Data API.
Our goal in providing this service is to enhance both performance and security, as well as to streamline the authentication process for application developers.
The Authentication Service can be used to access both regular Google accounts and hosted Google accounts (Google Apps). Although the login user experience is slightly different for hosted account holders, programmatically the process of managing authentication is the same for both types of accounts; no special steps need to be taken.