ASP.NET Tutorial/Configuration/authorization
Applying authorization requirements to a single file
<configuration>
<system.web>
<authentication mode="None" />
</system.web>
<location path="AdminPage.aspx">
<system.web>
<authentication mode="Windows" />
<authorization>
<allow users="DomainName\YourName" />
<deny users="*" />
</authorization>
</system.web>
</location>
</configuration>