Consider deprecating old utils API

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

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

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

The issue names no files, tests, or entry points. Start by locating the authentication configuration and any existing serialization or deprecation handling, then check how options are defined and tested. Done means auth serialization is controlled by enable_serialization, which defaults to false, with coverage for the enabled and default behaviors.

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