Optimize store for large datasets

**Description**
Currently auth lacks proper search support.

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

**Priority**: Low/Medium

Start by locating the authentication store and its current lookup or search entry point, then review how it handles large datasets. Clarify the configurable search behavior and sensible defaults before changing code. Done means authentication supports the agreed search configuration and its behavior is covered by tests.

Written by the indexing model from the issue text.