For each Sitefinity page there is an "Anonymous access" option in the page properties. Set this option to "No" and only authenticated users will be able to view the web page.
Next, create a new Role in the Administration section of the Sitefinity Admin. Only assign users you wish to view the page into this role.
Last, go to the permissions for the page and assign View permission to the new Role you created.
I think this should do it. Let me know if this isn't helpful.