Add unit tests for middleware

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

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

**Priority**: Low/Medium

The title asks for unit tests for middleware, while the body proposes configurable encryption for the store. First clarify the intended scope with maintainers, then locate the middleware and store entry points and existing unit tests; done should mean the agreed behavior is implemented and covered by tests.

Written by the indexing model from the issue text.