For background: the Rustic backup tool uses OpenDAL for cloud storage integration. The documentation is lacking on both sides. But I managed to reverse engineer that it expects the user to configure OpenDAL root & access_token (https://opendal.apache.org/docs/rust/opendal/services/struct.Onedrive.html#configuration) for OneDrive in a configuration file.

But there is no documentation on either side, what process needs to be performed to get an access token issued. Is this even something that a user should be exposed to? Or is it the application author's responsibility to provide a mechanism for requesting the access token?

But at the bare minimum, OpenDAL's documentation should document the expected format of this token (e.g. JWT token?) and reference relevant parts of Microsoft Graph API, and perhaps suggest a tool or library that can be used to request one.

Related discussion: #2129 (comment)