Support server-side widget JWT token generation via a backend credentials flow

The Widget JWT OAuth2 endpoint (identity.document360.io/connect/token) returns 400 invalid_client when called server-side with the Client ID and Client Secret from the widget configuration. All combinations of grant types, scopes, Basic Auth, and body params were tested — all rejected.

Use case: An enterprise in the media industry is building a custom SAP BTP integration in which the backend must generate a widget token before the widget loads in SAP Service Cloud V2. The browser-side widget SDK alone does not fit their server-driven architecture — the BTP backend needs to generate and pass the token as part of SAP session initialisation.

Request: A supported server-side token generation endpoint for the widget JWT — a service account or backend credentials flow that allows a trusted backend to generate widget tokens without relying on the browser SDK.