Classic ASP Active Directory Authentication

I am trying to use AD to authenticate users to enter secure areas of an Intranet site.
I know very little about AD.

I came across the following code which currently lets me verify a username/password combination.  If I enter good data, I see "authenticated".  If I enter bad data, I see "oops".

    <%
        'on error resume next
        strUser = Request.Form("username")
        strPassword = Request.Form("attempt")
        domain = "myad.domain.com"
        
        ' assume failure
        AuthenticateUser = false

        strQuery = "SELECT cn FROM 'LDAP://" & domain & "' WHERE objectClass='*' "
        set oConn = server.CreateObject("ADODB.Connection")
        oConn.Provider = "ADsDSOOBJECT"
        oConn.Properties("User ID") = strUser
        oConn.Properties("Password") = strPassword
        oConn.Properties("Encrypt Password") = true
        oConn.open "DS Query", strUser, strPassword

        set cmd = server.CreateObject("ADODB.Command")
        set cmd.ActiveConnection = oConn
        cmd.CommandText = strQuery
        on error resume next
        set oRS = cmd.Execute
        if oRS.bof or oRS.eof then
            Response.Write "oops..."
            AuthenticateUser = false
        else
            Response.Write "authenticated"
            AuthenticateUser = true
        end if
        set oRS = nothing
        set oConn = nothing
%>

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Great!

Problem:
Once a user is authenticated, how can I get a listing of the groups he/she belongs to?  I only want users that are part of a specific group to move on to the secure pages.