Trying to setup a user who was created in a separate domain

Every user in my domain is a part of a group I will call X_Users in the X.BAR.edu domain (as an example, that’s not the real name).

We have a new hire whose credentials are used at another branch and was created under just the BAR.edu domain.

I can’t add him to the X_Users group because it doesn’t allow global groups to have a cross domain member.

He logs into our systems fine with his account, I just can’t figure out how to give him access to Spark.

We run Win10 Pro, each user has a domain account at a user level in X.BAR.edu, except for the new guy who is located in BAR.edu

Does this make any sense or should I try to explain it a bit more?

I can’t create a new account for him since he uses the same account at his other location.

I will close this topic as this is most probably more related to Openfire than Spark.