How to determine "custom" role in delegate calendar permission is Write, DelegateWithoutPrivateEventAccess,DelegateWithPrivateEventAccess ms-graph-api

Question

We are giving calendar delegate permission to a user from Outlook Client using the steps mentioned in the images below.

Step 1:

Step 2:

If we set delegate permission to Reviewer, Author or Editor and try to get list of delegate users who have permission on owners calendar using Microsoft Graph API endpoint https://graph.microsoft.com/v1.0/users/{userprincipalname/userguid}/calendar/calendarPermissions from our application. It always returns "custom" in "role" property in response like in the below image.

Microsoft Graph API Response

Our problem is that we are not able to determine if the delegate user has "write" permission on the owner's calendar if the "custom" role is returned in the response as in all the above three permissions we are getting the same "custom" value in role property. Also, we are not able to determine it from any other property returned in the response.

Answer 1

List, create, get, update, and delete of calendar permissions is supported on behalf of only the calendar owner.

Getting the calendar permissions of a calendar on behalf of a sharee or delegate returns an empty calendar permissions collection.