Optimize core for large datasets

**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 error-handling paths, then determine which messages need improvement and how they should be tested; done means the relevant errors provide more descriptive debugging information.

Written by the indexing model from the issue text.