Improve auth performance

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

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

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

Begin by locating the authentication-related code under lib and reviewing its current error handling. The issue does not name a file, failing case, or performance measurement, so clarify the intended error cases and baseline first. Done should include more descriptive errors and evidence that the authentication path is faster.

Written by the indexing model from the issue text.