docs: C-1 — killing the SSO session logs nobody out

One user session carries a client session per application, so visiting the second app skips the login screen. Deleting the identity provider session leaves both application sessions untouched and both apps keep serving, because the identity provider, the application session and the access token each have their own lifetime.

That inverts the B-2 finding: there the app session was cleared and the surviving SSO session let the user straight back in. Either way, clearing one side leaves the other. It also means an identity provider outage is a single point of failure for logging in, not for already-authenticated users, and the failure arrives late and all at once.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/evidence/c1-multi-app-sso/01-baseline.txt

@@ -0,0 +1,11 @@
+=== 깨끗한 상태로 초기화 ===
+DELETE 1
+
+=== 기준선 ===
+  Keycloak 온라인 세션: 4
+  Redis 키: 0
+
+=== 두 앱의 구조 ===
+  app1.hyeonworks.com  →  BFF        (서버 세션: Redis + PostgreSQL)
+  app2.hyeonworks.com  →  oauth2-proxy (쿠키 티켓 + Redis)
+  둘 다 realm keycloak-patterns 를 쓴다