Back-end logout flow

[collinpreston]

User Story

The process flow for Keycloak's OpenID Connect logout flow should follow the process flow here: https://docs.google.com/document/d/17tJ-C2EwWoSpJWZKjuhMVgsqGtyPH0IN9KakXvSKU0M/edit#heading=h.qr1x27po61aq

Description/Context

https://docs.google.com/document/d/17tJ-C2EwWoSpJWZKjuhMVgsqGtyPH0IN9KakXvSKU0M/edit#heading=h.qr1x27po61aq

https://www.keycloak.org/docs/latest/server_admin/#backchannel-logout

https://github.com/mitodl/hq/discussions/2817

Acceptance Criteria

• When a user logs out of Keycloak, any MIT Open session associated with the user on the same device should be terminated.