Update core documentation

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

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

**Priority**: Low/Medium

No files or tests are named. Start by locating the middleware implementation, its configuration entry points, and the existing core documentation; first determine how middleware currently handles configuration and secrets. Done means configurable encryption has agreed defaults, is covered by relevant tests, and the documentation explains its use.

Written by the indexing model from the issue text.