Test if a user is authenticated before sending them to an authenticated site

Hi All,

I am developing an application for my company in ColdFusion mx 7.

They want a site that has anonymous access to be main site.

From this main site they want the user to try to use his windows authentication to get to an authorized site by a button click.

My goal is to set it up so that the user clicks a button from the anonymous site and gets sent to the authorized site only if they have access.

If they don't have access they get sent somewhere else in the anonymous site.

How can I test if the user is authorized before I send them to the site?

Any help would be greatly appreciated

Thanks

-Adesh