Refactor auth for better readability

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

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

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

Start by locating the authentication and parser error-handling entry points in the repository, then read how current failures are reported. Identify the parser paths whose messages need more detail and confirm the expected wording with the issue discussion. Done means the relevant errors are more descriptive and the affected failure paths remain functional.

Written by the indexing model from the issue text.