All logged-in users should be marked as authenticated

We use the built-in "authenticated" role in a matrix authorization strategy to grant all employees read-only access to our Jenkins setup. When we tried to switch from the OpenID plugin to google-login, we found out that read-only users were locked out. This seems to be because google-login doesn't grant users the authenticated role by default, though it should be given to all anonymous users. The attached patch resolved the issue for us.