docs: def _IsHomeDir(self, subject, token):
      """Checks user access permissions for paths under aff4:/users."""
      h = CheckAccessHelper("IsHomeDir")
      h.Allow("aff4:/users/%s" % token.username)
      h.Allow("aff4:/users/%s/*" % token.username)
      try:
        return h.CheckAccess(subject, token)
      except access_control.UnauthorizedAccess:
        raise access_control.UnauthorizedAccess(
            "User can only access their "
            "home directory.", subject=subject)