Add rate limiting for serialization

**Feature request**
It would be great to have import for auth.

**Use case**
Many users need this functionality for production deployments.

**Implementation idea**
Add a new config option `enable_import` with default `false`.

The title and body describe different work, so first clarify whether rate limiting for serialization or auth import is intended. No files, tests, or entry points are named; locate the relevant configuration and serialization or authentication entry points, then confirm that the requested behavior and the default `enable_import` value are covered.

Written by the indexing model from the issue text.