Improve error messages in auth

**Problem**
When working with middleware, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

The issue names middleware and authentication but does not identify files, tests, or a specific failing case. Start by locating the middleware error-handling entry points, then define the required messages and verify that the relevant error paths produce them consistently.

Written by the indexing model from the issue text.