Mapping AD security groups to roles

 Quite new to .NET authentication I have a question:
 In my app I want to able to split users up into three groups: admins, semi-admins and readers. I have created three AD security-groups that has the members of these three groups. In the code, I want to be able to say something like IsUserInRole("Admins"). The roles have to be mapped to the AD security-groups in the web.config, because I don't want to refer to them directly in the code. Can this be done in any other way than using a role manager? Can the security-group <-> roles relation be defined directly in the web.config or must I do it in the AzMan like explained here: http://msdn.microsoft.com/en-us/library/ms998336.aspx
Thanks in advance!

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