I am attempting to gain information on which users in Azure Active Directory have access to which Shared/Delegated Mailboxes. Unfortunately I cannot find any info on how to do this within the Graph API documentation - there are no endpoints listed for shared or delegated mailboxes.
I note that the following post from MSFT mentions that they are looking at having it implemented "by the end of the year" (and this post was back in 2015), however I am yet to find any information on MS Graph docs on this implementation:
Office 365 Unified API doesn't yet support access to shared mailbox content or membership. Access to content is on our roadmap, and something we hope to enable before the end of the year. We are looking at membership as well, but have no firm plans.
Get Members In Shared Mailboxes office 365
Any information on how I can go about retrieving Shared/Delegated Mailbox membership would be appreciated.
