Don't require API key for unauthenticated requests

[igoforth]

Is your feature request related to a problem? Please describe.
Thank you for making this package. My use case is an SDK to read content from public posts as an unauthenticated user.

Describe the solution you'd like
An ideal solution might be to categorize endpoints by whether they require authentication or not, and throw an error if the user accesses them without providing an API key

Describe alternatives you've considered
Splitting entities into authenticated and unauthenticated variants. Perhaps authenticated could be a subclass.

Additional context
None I'm aware of