OEP-42: Authentication

Hi everyone!

OEP-42: Authentication is now open for review!

This Open edX Proposal (OEP) describes how authentication in general should occur in the Open edX platform. This attempts to be the single source of truth for authentication.

The review period for this is: 2020/04/30 - 2020/05/15. Please comment on PR with your feedback.

Thank You,