I need assistance with integrating our backend service (built with Java Spring Boot) with a Microsoft Word add-in (built with Angular).

Current Setup:

• Our backend service creates a DriveItem for a Word document
  programmatically using the Microsoft Graph SDK for Java and uploads it to user’s OneDrive.

• The user is then redirected to a URL (webUrl) that opens the Word
  document in a new tab.

Requirement:

Our Office add-in, integrated into Microsoft Word, needs to send some type of information or an ID back to our backend service so that the backend can identify or reconstruct the associated DriveItem.

Thoughts and Attempts:

1. Query Parameter Approach:

• The backend service adds a query parameter like DocumentId to the
  webUrl.

• The add-in in Microsoft Word reads that query parameter and sends it
  back to the backend.

• Issue: Office.context.document.url doesn’t return the query string associated with the URL.

2. Custom Properties Approach:

• The backend service adds the DocumentId to additional data
  (FieldsValueSet) of the ListItem.

• The add-in reads the DocumentId from the document properties.

• Concern: I’m not sure if these custom properties can be read via
  Office.context.document.properties.

Question:
Am I missing another useful approach? How can I achieve this? Are there any other methods or best practices to send information from the Office add-in to the backend service for identifying the associated DriveItem?

This is urgent, so any help will be greatly appreciated.

Thank you!