Google Accounts, OpenID, and OAuth

App Engine features integration with Google Accounts, the user account system used by Google applications such as Google Mail, Google Docs, and Google Calendar. You can use Google Accounts as your app’s account system, so you don’t have to build your own. And if your users already have Google accounts, they can sign in to your app using their existing accounts, with no need to create new accounts just for your app.

Google Accounts is especially useful for developing applications for your company or organization using Google Apps. With Google Apps, your organization’s members can use the same account to access your custom applications as well as their email, calendar, and documents.