In the past, the first click free program allowed you to show subscription content to Google even if you required users to login. The only requirement was that when users clicked from Google to the article, they should be able to see the content without having to pay or login. After that first click from Google, you can require them to login. The only issue was that anyone wanting to see any article on a paid subscription site, would simply go to Google and click over to the article from Google to the site to get it for free.
The first click free program is old, it dates back past 2007 or further, as far as I know. In mid-2008, there was confusion if it could be used in web search as well and the ultimate decision is that is applies both to News and Web search.
For more technical details on this program, click here.