Refactor routes for better readability

**Problem**
When working with auth, 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 does not name files, tests, or an entry point. Start by locating the authentication route handlers and their current error messages, then determine the required cases; done means authentication failures provide clearer messages and the existing behavior remains verified.

Written by the indexing model from the issue text.