This ID uniquely identifies the user across applications - two different applications signing in the same user will receive the same value in the oid claim. Note that if a single user exists in multiple tenants, the user will contain a different object ID in each tenant - they’re considered different accounts, even though the user logs into each account with the same credentials. Notice the identities array that contains two GUIDs - those are the user account object IDs that I’ve allowed to access the site.