Promising second try, within PostgreSQL with pgsql_http extension.
We query directly Central's Odata service and get a json response :
SELECT content::json FROM http((
'GET', 'https://central.myserver.fr/v1/projects/1/forms/Sicen2020.svc/Submissions/',
ARRAY[http_header('Authorization','Basic bWF0aGlldS[...]OOGphYi9BQzIw')], NULL, NULL
)::http_request)
PostgreSQL offers a lot of json processing functions and in this scenario, we connect our database to a standardized stable interface !
To be continued