/usr/share/gvfs/mounts/admin.mount is in gvfs-backends 1.30.4-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 | [Mount]
Type=admin
# Add a dummy argument after pkexec, or '/bin/sh -c' will eat the first argument in '$@'
Exec=/bin/sh -c 'pkexec /usr/lib/gvfs/gvfsd-admin "$@" --address $DBUS_SESSION_BUS_ADDRESS' gvfsd-admin
AutoMount=true
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