Cross-domain SSO and global logout
Design SSO session continuity and global logout across a suite of 15 separate products on different domains (mail.x.com, docs.x.com, chat.x.com, plus 3 native mobile apps) sharing one identity provider. When a user signs in once they should be silently signed in everywhere; when they sign OUT (or an admin force-logs-out a compromised account), every product on every device must drop the session within seconds. Cross-domain cookies don't span the products, and mobile apps hold their own tokens. Discuss how silent sign-in works across domains, where the authoritative session lives, and how a single logout propagates to web AND native sessions fast.
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.