How did Quora implement their address book import?

How is Quora able to show me an invite page with all my Gma开发者_开发百科il contacts without even me logging into Gmail? Is there a way to pull email addresses without a password? Or is it that they are storing my address book, when I initially logged in?

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IMHO, you don't have to be logged in into Gmail for OAuth to work (which Quora is most probably using).

You need to be logged in at the moment of authorizing Quora via Oauth, afterwards you don't need to be logged in, since Quora keeps Oauth authorization internally, tied with your account. So until your OAuth gets invalidated, Quora most probably has access to Gmail contacts and entire Google shebang.

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You are likely already logged into Gmail, and when you click "Find Contacts", what Quora does is communicate with Gmail via OAuth. Google then asks you if you are sure you want to grant Quora access to your account data, which they will then send to Quora if you click allow.

If you weren't already logged into Gmail (or had a cookie saved) then Google would have to ask you to authenticate yourself first.