Office.context.mailbox.getCallbackTokenAsync not returning UPN property

Question

We have an outlook add-in that makes a call to

Office.context.mailbox.getCallbackTokenAsync

and opens a popup with our service. We use the returned jwt token to know which user to authenticated in our app. Recently we received a lot of reports of users not being able to login, and we found that the property UPN is not being returned anymore in the returned JWT token. We did not change anything in the add-in before the issue started happening. Did microsoft introduce some change that would make that property not be returned anymore? We still have SMTP that has the user email, but we are not sure if it is safe to use it instead of UPN.