Registration Token requirement can be bypassed by logging in with SSO

[matrixbot]

This issue has been migrated from #11067.

---

Description

Registration Token requirement (where you need a token given by an admin to sign up) can be bypassed by using a Third Party (OpenID) login service
I wish to have OpenID enabled on my private homeserver for the convenience of the people I give access to.
And I have registration tokens enabled since my Homeserver is private. (duh)

Steps to reproduce

• Create account via Third Party (Twitch, Google, Github, Whatever) with Registration Token requirement enabled.

Version information

• Homeserver: Would rather not provide publicly due to it being private, however it is self-hosted.

If not matrix.org:

• Version: 1.44.0

• Install method: Docker-Compose

• Platform: Ubuntu 20.04 Server running on actual hardware, Homeserver running in Docker Container