Problem with access denied redirect on form authentication

[fuginic]

Hi,

We are using the form authentication in a site, and we have add the grant in
a sub folder on this site, using nested web.config.
Only a "special" group have access to this folder, but when an user, not in
this special group, try to access to this folder, he is redirect to login
page.

It's possible redirect this user to a specif error page?
If yes, it's possible to do this operation with code, but only with
configuration?

A world of Thanks e ciao !!