Refactor auth for better readability

**Problem**
When working with data, 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 authentication and data-related error handling but gives no files, tests, or entry points. Start by locating the authentication flow and existing error-message handling, then clarify which cases need more descriptive messages. Done means the agreed refactor and error-message changes are implemented without changing intended behavior.

Written by the indexing model from the issue text.