The password is required once

[Eduardo Cavalcanti <ducavalcanti@recife.pe.gov.br>]

I'm using a PEAP-Mschapv2 autentication with freeradius.
When a client wants to autenticate for the first time, windows askes for 
the credentials where you must put your user name and password.
When this client wants to autenticate for the second time, windows 
doesn't ask his credentials (user name and password) again.

How can I obligate windows to ask the client credentials before every 
authentication????