I'm writing a mobile app, and I've reached a roadblock in trying to figure out how the owner of a Facebook profile could also be the same owner of a Twitter profile, based only on account info.
If John Smith
signed up for Facebook, but didn't input an e-mail address, phone number, or any other unique identifier, how is he distinguishable from the hundreds of other John Smith
Facebook users? More importantly, how can I know that he's actually the same John Smith
as on Twitter?
My current solution is:
When users sign up for my app, make them input an e-mail address and phone number.
This way...
Importing friends via phone contacts would be simple: check which of your friends' phone numbers already exist in your database.
Importing friends via Facebook would be possible: pull your friend's e-mail from Facebook (assuming he has one), and check if it exists in your database. If your friend's Facebook profile has no e-mail or phone number to pull, then I think there's no solution. Is there one?
And so on for importing friends from Twitter or any other social networking site.