I'm using Microsoft Entra ID to handle Single Sign-on.
The access token sent down has no UPN if the user logged in is a personal account, but does exist in work accounts.
Do personal accounts not have a UPN?
UPN is not available in personal accounts. The concept of UPN is associated with Work Accounts. You will need to adjust your application logic to handle these cases appropriately, perhaps by falling back on other claims when a UPN is not present. For personal Microsoft accounts (such as those used for services like Outlook.com, Xbox Live, etc.), the concept of a UPN is not typically applicable in the same way it is for organizational accounts. Personal accounts are usually identified by other means, like an email address or a username, which are not strictly UPNs in the AAD context.