Clever Membership Providers

I have recently been creating membership/role providers for use with the content management system where I work. We use active directory to authenticate users, however, we have some generic users that need to authenticate and we don’t really want to create them in our AD. The solution: Have my login page attempt to authenticate with ad and if it fails, have it check the sql membership provider. To do this, I override the Authenticate method for the login control on our login page like so:

protected void Authenticate(object sender, AuthenticateEventArgs e)
        {
            bool Authenticated = false;
            MembershipProvider provider;
            provider = Membership.Providers["MyAdMembershipProvider"];
            Authenticated = provider.ValidateUser(Login1.UserName, Login1.Password);
            if (!Authenticated)
            {
                provider = Membership.Providers["SQLProvider"];
                Authenticated = provider.ValidateUser(Login1.UserName, Login1.Password);
            }
            e.Authenticated = Authenticated;
        }

Of course, there may be some sort of security implication to this but I think its ok. If you know otherwise or know a better way of doing this, feel free to leave a comment!