The system context diagram has its main purpose to show interactions with users and other systems. As the focus is on the outside interactions, the "system to build" can be considered a black box in this view.
APPUiO Cloud is built to enable Single-Sign-On for developers and synchronize any user and team memberships to all enabled APPUiO Zones. A zone is basically an Openshift 4 cluster with the APPUiO Cloud add-on installed. There can be any number of zones from different IaaS providers.
"Owners" can configure organizations, users and teams. They manage team memberships and decide which of their developers can access which zones.