Authentication

I am not sure how to start this but herer goes. hopefully it makes sense. we run our own moodle instance on our network domain. We have another organization who would like to use moodle to offer training as well. We are all of the same organization. For our domain we may have 500 students who we auth/enrol using the csv file upload.  this works fine. however the other domain could potentially have upwards of 5000 users to enrol. We both  are on the same M365 tenant. From a basic perspective we would like to be able to auth/enrol based on M365. Is this possible. i.e. we only to auth and enrol users in courses. from my intial reading of this plugin this seems doable. If I am understanding this plugin, users would be able to log in to moodle itselt and also enrol in their specific course? Can moodle be a part of two domains (tenants) or does this matter? In my mind this would be so much easier than creating a csv file with various accounts, usernames, email addresses etc. Would I be correct in saying this? Or would the csv file upload still be the easiest method? Am I missing something here? We house moodle on our domain. (in a DMZ). When we login in to M365 on our domain we use the credentials provided by the other domains M365 tenant. Based on the above what are your thoughts? Thank you.