New features in CAS

Implemented a new setting called hijack user accounts, which allows existing accounts to be converted to authmapped accounts.

Now with CAS if you don't check "use drupal as account repository" and you do check the new "hijack" user setting, a user can alter their username after successfully authenticating with cas, and you can s till pre-create user accounts if you need to, (with the correct roles).

Hope that makes sense.