add error code to AuthError

I'm not able to do conditions for each error because there are just:
• name
• status
• message

I can not use name because it's not unique to each error.
It would make sense to introduce a unique error code that will help us write specific business logic in a catch block.

Example:
• name: AuthApiError
• message:Invalid Refresh Token: Already Used
• (new) code: refresh-token-already-used

This post is related to javascript SDK, and client, but it can be a general thing.