This is currently not on our roadmap. You can retrieve this value by making a call through the Graph API. If this is needed for your scenarios, please continue voting and we will review at a later date.Thomas Nolan commented
Please add this. Spent hours wondering why username wasn't a returned value when retrieving a token. Did not even cross my mind that it wouldn't be included and another trip to get the username was needed.
We have a sample for this use case here: https://github.com/azure-ad-b2c/samples/tree/master/policies/invite
Let us know what you think and if this fits your use case.