Getting contacts from Gmail/Yahoo/etc.

[jason2li]

I am developing a website, and I've seen some sites (like LinkedIn.com) where they allow you to enter your Gmail username/password, and it will get all of your contacts, so you can add them as friends or invite them to join the site.

How do they do this? I tried searching Google and this forum, but I couldn't find anything relevant.

Thanks!

ps. Here is a screenshot of what I'm talking about:

 

[urstop]

I think , once they have our username/passwords they can login into our accounts, go to the contacts page and get all the contact details from there.

This can be done programatically either simply by scraping of the page contents or a bit complex by actually posting requests to the yahoo / gmail servers.