How to correctly add members based on existing enterprise users

[JCGuarneri]

Novice question here, just getting started with ArcGIS API for Python. I'm trying to write a script to remove and re-add all non-admin users from my Portal to address issues from this bug. We add our Portal members using the "based on existing enterprise users" option.

My assumption had been that I would specify the "enterprise" as the provider. However, while investigating the properties of our users to make sure I have the script correct, I noticed that all of our members have "None" for provider (see below). "None" is not one of the provider options in the documentation. What is the correct way to specify existing enterprise users when adding new members, and not the enterprise logins via SAML?