Customized login auth plugin

[fefrei (Felix Freiberger)]

Discourse’s SSO support does exactly this:

DiscourseConnect - Official Single-Sign-On for Discourse (sso)

(Feb 2021) ‘Discourse SSO’ is now ‘DiscourseConnect’. If you are running an old version of Discourse, the settings below will be named sso_... rather than discourse_connect_... The DiscourseConnect protocol allows you to completely outsource all user registration/login in Discourse. The Problem Many sites wishing to integrate with a Discourse site want to keep all user registration in a separate site. In such a setup all login operations should be outsourced to that di…