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        public User GetAuthenticatedUser()
        {
            User user = base.GetAuthenticatedUser(new WindowsPrincipal(WindowsIdentity.GetCurrent()));
            string[] tmp = user.Name.Split('\\');

            DirectoryEntry entry = new DirectoryEntry("WinNT://" + tmp[0] + "/" + tmp[1]);
            user.FullName = entry.Properties["FullName"].Value.ToString();
            user.Groups = entry.Properties["Groups"].Value as string[]; 

            return user;
        }					

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WindowsIdentity userIdentity = WindowsIdentity.GetCurrent();
string fullname = userIdentity.Name;
string[] userGroups = userIdentity.Groups.Select(identity => identity.Translate(typeof(NTAccount)).Value).ToArray();