CloudKit sharing how to find out the user who shared the CKRecord

If several users are sharing records with .readwrite permission with me, how can I find out who shared which CKRecord? I know user information is confidential information. But I need to be able to find out who shared so I can react to the shared record by either modifying or ignoring. I cannot find anything in Cloud Sharing website by Apple. Can someone give ideas/ponters?

Of course I can find out who shared the record, when I get a sharing message/email from user. But is there a programmatic way to find out who the user is from the shared CKRecord.

CloudKit sharing how to find out the user who shared the CKRecord
 
 
Q