Give an URL which needs authentification

Hi!
For a specific page, which needs authentification (and so permissions), I would send to my site users an URL where :

1. If the user is not authentified, the user/login page shows and redirect to the real page after login ;
2. If the user is already authentified (by session/cookie), the page shows.

I try to make the URL as :

http://www.domain.com/user/login?destination=mypage

It works when the user is not authentified but shows an "Access Denied" when user is already authentified.

So if you already meet the same problem, ...many thanks for your help...