

Should SSO solutions find existing users by that person from other sites? - flexd

It's a social world out there and anything and anyone are expected to be connected up and with that the easiest way of having people try out your service is by having Facebook/Twitter/Linked In logins.
The old 'password approach' is no longer such a feasible option.<p>But my question is: Do you feel that there is a need for multiple sign on solutions per user? If i have the option of signing in with Facebook and Twitter should the Twitter sign in automagically find my Facebook-created user and link those two up as well? 
I'm just wondering as it's something i have been annoyed at for a while.<p>Or is it fine that multiple signup methods will also create multiple users? 
The data returned from all these sites should have some sort of common data it should be able to find the others users by?
PS: Sorry if some sentences seem incoherent, English is not my native language :-) and this was supposed to be a Ask HN post.
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petervandijck
The common data is the email. Yes, it's possible, there are companies that do
this and sell the information for marketing purposes.

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flexd
I kind of knew/suspected the email would be the common data so it's not really
a problem doing so but does it really matter? Is it needed or do most people
just sign in with one site and stick to that?

I was actually more wondering what is common practice, i don't have any
popular sites requiring logins myself so i was wondering what is the norm. Do
your system link multiple accounts with the same email then?

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flexd
Actually, Twitter does not seem to provide a email.

