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 names no files, tests, or entry points. Start by locating the authentication route and its error-handling paths; done means the relevant failures produce more descriptive messages and the affected behavior is covered by tests.

Written by the indexing model from the issue text.