Question

The problem I see with single login services, is that if you login once using Facebook, once using Twitter, and once using LinkedIn – you have three different accounts. Everything would be fine, if Twitter was giving an email address. So, how do you fix it?

Answer 1

I have the same problem and I was hoping the clever folks on SO would have an elegant solution. All I can think of doing is :

1. User logs in with LinkedIn
2. Check the user table to see if they have an account using their LinkedIn id
3. If not, ask them for their email address before logging them in
4. When we have the email address, check to see if they already have an account using their email address
5. If they do, add their LinkedIn ID to this record and log them in
6. If they don’t, create a new record and log them in

This means that each user record needs fields for every possible account, or more correctly use a link table connected to their local user id with a record for each account they log in with.
It also defeats the benefit of a simple OpenId login because the user has to register their email the first time they login with a new OpenId account.

Like I said, elegant it ain’t, but it is the best I can think of.