MAAS 3.4 installed with deb fails to start the rack due to permission error

[Jacopo Rota]

MAAS 3.4 rack controller fails to start after a fresh installation with deb on ubuntu 22.04 due to

Traceback (most recent call last):
  File "/usr/sbin/rackd", line 33, in <module>
    sys.exit(load_entry_point('maas==3.4.0rc1', 'console_scripts', 'rackd')())
  File "/usr/lib/python3/dist-packages/provisioningserver/server.py", line 95, in run
    runService("maas-rackd")
  File "/usr/lib/python3/dist-packages/provisioningserver/server.py", line 90, in runService
    UnixApplicationRunner(config).run()
  File "/usr/lib/python3/dist-packages/twisted/application/app.py", line 370, in run
    self.application = self.createOrGetApplication()
  File "/usr/lib/python3/dist-packages/twisted/application/app.py", line 432, in createOrGetApplication
    ser = plg.makeService(self.config.subOptions)
  File "/usr/lib/python3/dist-packages/provisioningserver/plugin.py", line 276, in makeService
    secret = MAAS_SHARED_SECRET.get()
  File "/usr/lib/python3/dist-packages/provisioningserver/utils/env.py", line 64, in get
    self.path.read_text(encoding="ascii")
  File "/usr/lib/python3.10/pathlib.py", line 1134, in read_text
    with self.open(mode='r', encoding=encoding, errors=errors) as f:
  File "/usr/lib/python3.10/pathlib.py", line 1119, in open
    return self._accessor.open(self, mode, buffering, encoding, errors,
PermissionError: [Errno 13] Permission denied: '/var/lib/maas/secret'

How to reproduce:

Install the region controller:

apt-add-repository ppa:maas/3.4-next
apt update
apt install maas-region-controller
maas createadmin

Install the rack controller on another machine:

apt-add-repository ppa:maas/3.4-next
apt update
apt install maas-rack-controller
maas-rack register --url http://192.168.122.XXX:5240/MAAS --secret $SECRET