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I just come to realize that I can login to Stackoverflow with my Facebook account and still get my same SO account as when I log with Google OpenId (which i always used before) but... I never added Facebook OpenId to my SO account (in my profile I only get openid : Google (xxxxxx@gmail.com).

Also, when I log in with Facebook and I click to logout, my Google account is displayed like this

You’re a registered user.

You have the following credentials associated with your account, which you can use to log in at any time:

Google (xxxxxx@gmail.com)

Nothing about Facebook there even if I logged in with it.

Can someone explain how's that working ?

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Do you maybe have a cookie persisting from a different Stack Exchange site? What happens if you log out of everything and clear your cookies? –  shanethehat Jul 28 '11 at 15:57

2 Answers 2

up vote 8 down vote accepted

For certain trusted providers (Google and Facebook are two of them), we will store their assertion of a user's email.

If you subsequently login with a different trusted provider which asserts the same email, we'll assume you just forgot which provider you originally used and log you into your existing account rather make a new one (since we're sure it's the same person, through ownership of the same email).

The list of trusted providers is subject to change, but the basic requirement is "validates user emails at account creation time".

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I know this is an old answer but what would happen if I change my Facebook email (e.g. Facebook rolled out their own @facebook.com emails and I decided to remove my old email from FB) and I clicked "login with Facebook". Does this mean I would be created as a different user? –  KerrM May 21 at 14:14

Is it possible you're simply still logged in from the cookie of your last session? Unless you explicitly log out of Stack Overflow, you'll remain logged into the site even if you log out of your provider. That way, you can even access your Stack Overflow account without logging into your provider at all (I rarely log into mine, for example).

Note that account association does not operate strictly on the OpenID provider, since Google's OpenID string changes depending on what domain you are on. However, I don't believe this is involved in this scenario, since that matching is done for associating accounts across the network and not for actually logging into the website.

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No, I logged out from everything (Google, Facebook, Stackoverflow), then I log in with Facebook, and still get my right SO account where nothing is linked to/from Facebook, and never used Facebook to log in before. I just don't understand how this works. –  MaxiWheat Jul 28 '11 at 15:40
    
Hm. How curious, then. Let's see if a dev can lend some insight into that. –  Grace Note Jul 28 '11 at 15:43
    
I don't know if that as to do that my facebook username is my google email (gmail) –  MaxiWheat Jul 28 '11 at 15:46
    
Well, that would affect account association (I know it to work exactly in that fashion, though with a different provider than Facebook), but I wouldn't think it'd strictly affect the actual act of logging in. It's likely to be the case, but a dev will still need to drop in and provide a clearer explanation as to the link. –  Grace Note Jul 28 '11 at 15:52

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