Hi,
best approach to do that is to put custom authorization in the web.config e.g.
<system.web>
...
<authorization>
<deny users="?" />
<allow users="*" />
</authorization>
....
</system.web>
and then expose the pages you want by doing this
<configuration>
...
<location path="Default.aspx">
<system.web>
<authorization>
<allow users="*" />
</authorization>
</system.web>
</location>
//Put other pages here
...
</configuration>
You can read more about this here "
Authorization for a Web application".
Regards