Update auth documentation

**Description**
Currently core lacks proper serialization support.

**Proposed solution**
Add configurable serialization with sensible defaults.

**Priority**: Low/Medium

Start by locating the authentication documentation and the core code responsible for serialization. Clarify which data needs serialization, the supported formats, the configuration surface, and the intended defaults. Done means the documentation and implementation agree on configurable serialization behavior, with validation for the chosen defaults.

Written by the indexing model from the issue text.