Set the folder permission which is out of IIS

I need the settings in web.config file of my a开发者_开发知识库sp.net application through which i can set permission for particular folder outside IIS. I need this functionality through settings in web.config.

Edited: I need to know that how can we apply impersonation in web.config file

thanks

regarding the second part

<configuration>
    <system.web><identity impersonate="true"/></system.web> 
</configuration>