Add unit tests for auth

**Problem**
When working with types, 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 names no files, tests, or entry points. Start by locating the authentication type validation and any existing auth tests, then confirm which error cases need coverage and what more descriptive messages are expected. Done means the relevant unit tests pass and the requested error details are verified.

Written by the indexing model from the issue text.