Improve auth performance

**Problem**
When working with core, 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 core authentication error-handling path and clarify which performance problem and messages are in scope; done should mean the scope is resolved and the resulting behavior is covered by tests.

Written by the indexing model from the issue text.