Windows Authentication - Problems

Good afternoon everyone ...
I have an asp.net application (not MVC) and want to use the windows authentication.
I have a part that only administrators can access and any other one.
Adm directory put a web.config like this:
<? xml version = "1.0"?>
<configuration>
   <system.web>
     <authorization>
       <allow roles="rolesAdm" />
       <deny users="*"/>
     </ authorization>
   </ system.web>
</ configuration>
Whenever I do something adm directory, the prompt asks for authentication.
I wanted once authenticated, the authentication did not ask for more.
...