setting up form authentication for a specific folder

I have an "Admin" folder in my application that will include pages that I would not like to have anonymous access to.  When a user attempts to load a page that resides in this folder, I would like to redirect them to a login page. Here is what I have in my config so far.
 
<authentication mode="Forms"> <forms loginUrl="~/Admin/Login.aspx" timeout="2880" > <credentials passwordFormat="Clear"> <user name ="isaac" password="****"/> </credentials> </forms> What do I need to add to get the functionality I am lookign for. Thanks

 
 
 
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