Unsetting PHP_AUTH_*

Hello to all I've the variables $PHP_AUTH_USER and $PHP_AUTH_PW set and I want to unset them because I check if they're set or not in order to show the authentication dialog box. The unset command appears not to be working with them (even if I try doing unset($GLOBALS['PHP_AUTH_USER'])...) Any suggestion? Thanks a lot! Danny Este correo electrónico contiene información privada y confidencial. Si usted no es el destinatario del mensaje no está autorizado a leerlo, copiarlo o difundirlo. Si lo ha recibido por error, por favor contacte con el remitente y destruya su contenido.?Privileged/confidential information may be contained in this e-mail. Any reading, copying o dissemination of this communication by persons or entities other than its intended recipient is prohibited. If you received this in error, please contact the sender and delete it.