Controlling access to external site via cck node link.

Hi All, I've created a cck node with a text field which I will enter a link to launch an external web site url.... I want to know if there's a way to control which users/groups can have access to that external url when the link is clicked. I think I might be able to control who "sees" the link on the page BUT I want the link to be visible to all users BUT only allow that link to launch or activate ONLY if user is authorized.

So, when a user who has not logged in and clicks on that link on the cck node they will be prompted to login or register in order to launch external site...

I would appreciate any comments/suggestions to any solutions that would achieve above.

Joe