This is a easy and quick task! We think Javascript is needed but you can use another language if you think it can do the job!
The script:
Deny acces from all webpages except 1 (including type ins)
Send denyed to one site (example [login to view URL])
and if the visitor are comming from the correct page he is allowed to see the content of the file/site/script where the code is inserted!
The code can be inserted in all php or html pages