Consider adding `cause` as an alias to UnauthorizedError

[Simon Schick]

Describe the problem you'd like to have solved

The canonical property name is cause and this was also recently added to the NodeJS error constructor and is used in browsers as well

Describe the ideal solution

I propose adding cause in addition to inner to align these and to keep it a non-breaking change.

Alternatives and current work-arounds

None really, it's not that hard of an issue I think.

Additional context

None.