As a Developer, I can rely on a standardized APIClient class to authenticate requests on any reader

[gabrielleberanger]

WHY
Today, each reader uses its own authentication method: either a client class or a helper method.
Available client classes are available under the nck/clients directory (after the refacto, clients shared by several sources will appear under nck/clients/, and source-level clients will appear under nck/readers/<source>/client.py).

HOW

Long term goal
Create a unique APIClient class, that could handle the authentication process for all readers.
Today, a standardization effort has been undertaken with the creation of the APIClient class ; however, this class is only used by Yandex readers today. As we might not be able to standardize all authentification methods into a single one (some APIs are quite specific), we suggest to pursue the below preliminary goal as a start.

Intermediary goal
Group sources sharing a similar authentication process (e.g. Google sources) into a single client class.