What would be the correct workflow to have multiple be able to use a device via Username/Password?
Having the user object identified via the view variables is simple enough, but the Global User is seemingly locked to the enrolled user.
If the end users have connectivity while switching users, I would suggest having the users logout and re-login so that your user object is always the enrolled user without having to track the current user separately.
If the users will be offline while they need to switch who is enrolled, then you will need to track the current user in a separate way from the global user object as the global user will always be the enrolled user.