hub: fail open in case an invalid acl permission is specified

kobo/hub/__init__.py

@@ -30,6 +30,16 @@
  raise ImproperlyConfigured("Invalid permissions on '%s'." % dir_path)
 
 
+if hasattr(settings, "USERS_ACL_PERMISSION"):
+ acl_permission = getattr(settings, "USERS_ACL_PERMISSION")
+ valid_options = ["", "authenticated", "staff"]
+ if acl_permission not in valid_options:
+ raise ImproperlyConfigured(
+ f"Invalid USERS_ACL_PERMISSION in settings: '{acl_permission}', must be one of "
+ f"'authenticated', 'staff' or ''(empty string)"
+ )
+
+
 if getattr(settings, "MIDDLEWARE", None) is not None:
  # Settings defines Django>=1.10 style middleware, check that
  middleware_var = "MIDDLEWARE"