Finding friends through twitter, facebook, gmail, etc

Question

Hi,

I have a web app, where I ask for a user's:

• Email address (required)
• First/Last name (optional)
• Twitter handle (optional)

I'd like to allow them to find friends also using my service - if I understand correctly, I can offer the following methods:

• Given their email address, try to find their contacts. This may be based on their email provider. For example, if they're using gmail, I think gmail offers an api where I can search for a user's contacts. I take that list of email addresses, and check if any of them are also users on my site.
• If they supply their twitter handle, I can use the twitter API to get a list of users they are following.
• I can ask them to enable Facebook connect. If they connect, then I'll get their facebook ID. I can use this ID to fetch all their facebook friend IDs. I can check if any of those ids also match users on my site, that also setup facebook connect.
• Just a general search by first+last name.

I think those are the basic ways for friend finding - am I missing anything obvious? I'm most curious about the gmail method - do any other email providers offer something similar, or is there some open standard for that?

Thanks

Answer 1

I don't think gmail will give out a user's contacts, without them letting you (either by providing their password so you can log in as them, or by giving permission via e.g. OAuth). You can probably get the people they follow on Buzz via their profile.

OAuth is the usual method for access - I know twitter and gmail support OAuth.