[IO.File]::WriteAllBytes($File, [Convert]::FromBase64String($Data))
  Log_Todo ("need to set permissions correctly on ${File}; not sure what the " +
            "Windows equivalent of 'umask 077' is")
  # Linux: owned by root, rw by user only.
  #   -rw------- 1 root root 1.2K Oct 12 00:56 ca-certificates.crt
  #   -rw------- 1 root root 1.3K Oct 12 00:56 kubelet.crt