Improve error messages in lib

**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-related code under lib and tracing where its current errors are created or returned. Review the existing error-handling paths and any nearby tests, if present. Done means the relevant authentication failures provide more descriptive messages and the affected behavior is covered by tests.

Written by the indexing model from the issue text.