Enhance the OAuth 2.0 request when using the External URL element

Issue:
Korbyt's External URL element hardcodes the Files.Read scope into every OAuth 2.0 request it sends, regardless of provider or target resource. This works fine when the target is a Microsoft Graph resource (SharePoint, OneDrive, Excel embeds), but breaks for any non-Graph OAuth target, since Entra rejects the request with AADSTS65005 ("scope doesn't exist") when the app registration on the receiving end has no Files.Read scope defined.

Update the external URL element to support OAuth2.0.