Update auth documentation

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

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

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

Review the authentication and helper-related documentation and error handling first; the issue names no file, test, or entry point, so locate the relevant material in the repository. Done means the scope is made concrete, the documentation is updated, and the resulting error messages are more descriptive, with existing coverage checked.

Written by the indexing model from the issue text.