if you go to:

> 
> <http://www.stackoverflow.com> you'll be redirected to
>  <http://stackoverflow.com>
> 
> 
> <http://facebook.com> you'll be redirected to <http://www.facebook.com>
> 
> 
> 

the problem is that if a user **authenticates** to: 

<http://www.example.com>

and after goes to <http://example.com> he will not be authenticated (because the domain is different, I guess)

I noticed that stackoverflow and facebook redirect to the domain with/without www

anybody knows how this is done ?