Currently the Authorization API (https://docs.microsoft.com/en-us/rest/api/authorization/classicadministrators/list) returns the email address which is not unique and puid/netid of the user which is absent in the user resource in Graph API. (https://docs.microsoft.com/en-us/graph/api/resources/user)
Only the Azure Portal can resolve it using an internal version of the old Graph API (1.61-internal)
Please either:
1. Add the puid/netid to the user resource in the Graph API
2. Add the objectId of the user resource to the Classic Administrator API

Thank you