Add access control

[danb35]

As it now stands, the self-service password page is accessible anywhere the webserver can be reached--it isn't, and can't be, restricted to the LAN or other "green" networks. The initial purpose of this project was to allow remote users to change their passwords; there are other existing mechanisms for local users to do so (like the user settings page in Cockpit)--but nonetheless this could be a useful enhancement.