How to authorize sub section of an XMLSIteMap

Question

Hi,

If i have a XMLSiteMap in an ASP.NET application, and there is one section which is allowed for admin, and a part of that section (sub section) to be available for a user, how can this be configured in web.config ? If i use the configuration, it allows me to authorize admin to use the section. How do i then allow only the subsection (in a different location) to user role ?

Thanks.