Update lib documentation

**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.

Start by locating the authentication error-handling code under lib and read the related callers and tests, if present. Clarify which auth failures need more descriptive messages and what wording or coverage counts as done before changing behavior.

Written by the indexing model from the issue text.