Howto use Google Accounts as login

I'm thinking about using Google Accounts as a user verification for a service I'm developing. This will be a client and server. I'm hopin开发者_如何学Gog to be able to use the already signed-in Google Account on the Android phone and use that as a verification on my server.

Where can I find information about this?

Is it possible to use the already signed-in account on the phone or do I have to re-sign-in in my application?

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There's a class called AccountManager which acts like a registry for the users online account. I think this is what you are looking for.

There's also something called Federated Login for Google, which allows users to login using their Google Account. Its more like OpenID