Pin the session-state architecture: the browser carries only an opaque
crypto-random session id in __Host-portal_session, signed with
SESSION_SECRET. The payload (userId, audience, curated claims, encrypted
tokens, timestamps) lives in self-hosted Redis, accessed via the standard
express-session + connect-redis pair under the NestJS Express adapter.
The id_token / access_token / refresh_token tuple is encrypted with
AES-256-GCM before being stored - per-record IV, GCM auth tag - using
SESSION_ENCRYPTION_KEY. A Redis snapshot or memory dump alone is not
enough to forge a working session; the encryption key must also be
compromised. Tampered or wrong-key records are rejected and audited.
TTL policy: idle 30 min sliding (TTL refreshed on each request) +
absolute 12 h (checked in a global interceptor, triggers DEL on expiry).
Topology: Redis Sentinel (3+ nodes) in prod with TLS and ACL; single node
in dev. Operational specifics deferred to a phase-3 infrastructure ADR.
Revocation is immediate (DEL session:{id}). A secondary index
user_sessions:{userId} supports per-user listing and force-logout. No
PostgreSQL mirror; historical trace lives in the future audit-log ADR.
decisions/README.md index updated. CLAUDE.md gains an explicit 'Sessions'
line pointing to ADR-0010.
Julien Gautier