Can't connect to Google Cloud API (others than those with specific nodes)

Hi,
I’m trying to use Google Document AI to make an invoice OCR and entity extraction app.
The API is great and I’d like to use it through knime.
There is specific knime nodes for some google API like sheets, drive, analytics, but not for all APIs.

I tried two ways :
A/ authenticate with “Google Authenticator” node then use “GET request” node to interract with the API. But I can’t get a Token out from “google authenticator” so I can’t write GET requests and I’m stuck.
B/ I tried to use the three “Oauth2 authenticator” nodes to connect to google services without success (so many tries with so many differents config than I can’t list them here).

Has anybody successfully used other google API ?
Thanks, have a good day !