Unable to run container with userns in auto mode

[abpetrov]

I am trying to run a container with the following userns config, to create a particular mapping between a user on the host and the user in the container:

      driver = "podman"
      config {
        image = "docker.io/library/cassandra:4.1.10"
        ports = ["cassandra"]
        userns = "auto:uidmapping=999:20999:1,gidmapping=999:20999:1"
      }

However, looking at podman inspect, it seems that the podman driver ignores the config

          "HostConfig": {
...
               "UsernsMode": "",

Is there something I miss, I followed https://docs.podman.io/en/latest/markdown/podman-run.1.html#userns-mode to construct the userns option.