授予我网站访问权限的最佳和最简单方法是什么（OAuth，OpenID ...）

I'd like to grant access to my site via Facebook, Twitter and so on. I will definitely need the user's email and hopefully his avatar image. I see the following algorithm:

1. User clicking on "access via Facebook (or anything)" button
2. Browser shows a pop-up with Facebook (or anything) login and password inputs
3. User types in his login/password pair and clicks "Sign-In" button
4. Something (it is not clear for me how) calls my script like mysite.com/login.php?token=token_it_self&email=john.doe@gmail.com&avatar=http://facebook.com/images/12345.jpg

Probably there are any tools to make this routine clean and easy providing most common social networks (Facebook, Twitter, LinkedIn...)? Of course free tools will be much more appreciated.