[Plugin: Shibboleth] Issues using apply_filters on Shibboleth attributes

The new release of the Shibboleth plugin supports attribute manipulation via the WordPress apply_filters technique, which is great. However, it doesn’t seem possible to use this approach to modify a username; I need to set the username to be EPPN but *without* any scope. I thought this would be possible via apply_filters in the user_login line of shibboleth_update_user_data but I think the code in shibboleth_authenticate_user overrules this – is there a way around this?

Also, a general point which I can work around for now but perhaps could be solved for a future version: calls to apply_filters only pass a single attribute value, so it is not possible to write a filter that combines/processes multiple attributes.