Add rate limiting for filtering

**Description**
Currently validation lacks proper encryption support.

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

**Priority**: Low/Medium

The title asks for rate limiting, while the description asks for encryption support; resolve that mismatch before locating the validation and filtering entry points in the repository. Review how configuration and validation are currently handled, then define tests for the selected behavior and its defaults. Done means the agreed requirement is implemented and covered by tests.

Written by the indexing model from the issue text.