Google has released an Account Authentication service which is very similar to Microsoft’s Passport service. Other Web sites will now be able to get access to Google services with the proper user authentication. Here is an example of where this could be useful:
Users of Google Calendar manage their schedules, add, update, or delete events, and share calendar information. In this scenario, you have a web application that communicates with the Google Calendar service. You want your application to display Google Calendar data and manipulate that data on behalf of your users. To do this, your application needs to get access to your user’s Calendar account. Before accessing the account, the application must request authorization from Google. It does so by calling the Google Authentication URL and supplying some required information, such as the name of the service to be accessed. If Google accepts the request, a Google page is displayed that prompts the user to log in and either consent or refuse to provide access to their Google account. If they consent, Google redirects the user back to your web application and supplies an authentication token for the requested service. The web application can then make requests directly to the Google service, referencing the token in each request.
Eventually sites will be able to register with Google and become “trusted”. If a site is trusted then you will not be prompted each time that an attempt is made to access information. With Google constantly releasing new services it is important that they allow users to access their Google data in services offered by other companies.
News Source: Googling Google