No "Preemptive Bearer Token" in REST model

I noticed that when creating an npm proxy, there was an option in the UI to pick "Preemptive Bearer Token" as an authentication method. This option is not available in the REST model, so users must guess or investigate code to determine the value (assuming the value is allowed in REST, I did not check).

I assume this was not intentional, but I couldn't find out what this does in documentation either, so I could be wrong. Filing a ticket for analysis.