The LinkedIn API Login is common question that many LinkedIn developers have. The LinkedIn API Login makes it super easy for developers to authenticate users by using the LinkedIn API Login for users to login to their apps or other uses. Here’s some more information about the LinkedIn API Login directly from LinkedIn. It essentially lets you use the LinkedIn login for your apps.
You use the inside of the IN/Login template to echo out the person’s name in the sign up form. More importantly, you’ve added a hidden variable, linkedin-in, to pass the member id. This is the value you should store to identify the person in future page requests.
This generates a Sign In with LinkedIn button and triggers the onLinkedInAuth() function upon completion. That function makes an IN.API.Profile() API call for the current viewer and provides you with the member id in the callback function. You can then use the AJAX framework of your choice, such as Dojo, YUI, or jQuery, to pass that value back to your server.