feat: the room may use the church Wi-Fi and may not read its password

These are shared computers in rooms full of people, and in a stock Plasma
desktop "use the network" and "read the network's password" are much
closer together than they look.

Measured on Debian 13 with NetworkManager 1.52 and Plasma 6.3:

  * org.freedesktop.NetworkManager.settings.modify.own ships as "yes" for
    an active session — no prompt, no administrator. It covers any
    connection whose connection.permissions names that user, and a Wi-Fi
    network added from the desktop is created exactly that way. So a
    password a teacher types in is readable by the next person to sit
    down.
  * the applet offers "Show Network's QR Code" on every saved wireless
    connection, and the QR code contains the pre-shared key.
  * that action, and the "Configure…" beside it, are contextual actions in
    ConnectionItem.qml and do NOT consult
    authorizeControlModule("kcm_networkmanagement"). The Kiosk key gates
    the toolbar button only. Hiding buttons was never going to be the
    answer.

Every one of those paths ends at NetworkManager's GetSecrets, so that is
where this is answered. A polkit rule refuses settings.modify.own,
settings.modify.system, both wifi.share actions and the machine-wide
settings, for the classroom user by name.

Deliberately NOT refused: network-control, wifi.scan and the
enable/disable actions. None returns a secret, and they are what
connecting and seeing a network are made of. Automatic reconnection does
not go through polkit at all — NetworkManager does it as root — so nothing
here can stop the room coming back on the network after a reboot, which is
the property that matters most on a Sunday.

An administrator's account and root are untouched, and the override route
is the same one the sleep rule has.

classroom-wifi is the other half, and it is a requirement rather than a
convenience: it provisions the church Wi-Fi as a SYSTEM connection, with
no connection.permissions, psk-flags=0 and a 0600 root:root file. A
connection the machine owns is one nobody in the room can read. Verified
against real NetworkManager in the lab — the classroom account gets
"Permission denied" on the file, "--" from nmcli and "Insufficient
privileges" from GetSecrets, while autoconnect stays on.

There is deliberately no teacher-facing join dialog. Anything that lets
the room add a connection lets the room own it, and an owned connection is
a readable one; docs/networking.md says so rather than leaving it to be
rediscovered.

The rule is plain JavaScript, so the test evaluates it with polkit's
objects stubbed and asserts both halves: which actions come back NO, and
which are left alone. What it cannot test is the last mile — polkit
resolves a subject through logind and a container has no graphical seat
session, so every check there is denied for reasons unrelated to this
rule. That one is a physical check, and it is written down as one.

Co-Authored-By: Claude Opus 5 <[email protected]>

config/plasma/xdg/kdeglobals

@@ -32,6 +32,22 @@ action/help_report_bug=false
 action/help_about_kde=false
 action/help_contents=false
 
+# The network applet reads this one before it draws its own settings
+# button and its "Configure Network Connections…" entry — see
+# main.qml, which calls
+# KAuthorized.authorizeControlModule("kcm_networkmanagement").
+#
+# This is only the first of two layers, and on its own it would be
+# security theatre. The applet ALSO puts "Show Network's QR Code" and
+# "Configure…" on every saved wireless connection as contextual actions,
+# and neither of those consults this key — measured on Plasma 6.3. The QR
+# code contains the pre-shared key. What actually refuses them is the
+# polkit rule in org.ekklesia.classroom.network.rules, which answers at
+# NetworkManager rather than in a menu. This key is here so that a teacher
+# is not shown doors that will not open.
+[KDE Control Module Restrictions][$i]
+kcm_networkmanagement=false
+
 # Not immutable. Marking this group [$i] froze the colour scheme so hard
 # that `classroom-theme light` changed the running session and then lost
 # the change at the next start — measured. These are defaults for a room