For this setup I haven’t checked the feasibility yet. The opposite (Meteor login with Moodle accounts) would be much easier.
However MOODLE supports OAuth2 workflows and you may check out the DEMO to play around with it: https://moodle.org/demo/
You definitely have to read through the OAuth2 standard:
but a good starting point is also this resource: https://oauth.net/2/
If you also need to exchange data beyond just user accounts, you need to read about LTI:
If you realize, that you need to run your own OAuth2 server, I successfully managed to wrap it into a single Meteor package:
Hope this is a good starting point.