Actually saying that, not sure if the built in authentication supports this yet.
Add Origin header to OAuth 2.0 flow - Help - Postman
Therefore you may have to use sendRequest in a pre-request script to generate your token instead where you should be in full control of what headers you send.
Or you could craft a Post request with all of the settings. I prefer the pre-request script as you can handle the token expires with simple IF statements.