Pin the MFA policy: enforcement lives in Entra ID Conditional Access at
the tenant level (org IT responsibility) - the application code does not
implement MFA mechanics. The BFF performs a defense-in-depth sanity-check
on the id_token amr claim at session creation; sessions without evidence
of multi-factor authentication are rejected. The accepted amr values are
maintained in a small in-source list and reviewed on cadence.
Step-up MFA is designed-in for v1 but dormant: a @RequireMfa() decorator
and a RequireMfaGuard ship in the codebase, the session payload carries
mfaVerifiedAt, and the SPA HTTP interceptor handles the 401 + claims
challenge round trip. No v1 route is annotated, since v1 has no admin UI
or other operations sensitive enough to require fresh MFA. The hooks are
kept alive by automated tests so they don't drift.
Authentication Context Classes (ACR-based step-up) are not used in v1;
they remain a future option if specific operations later demand them.
Service-account / app-only flows are out of scope.
decisions/README.md index updated. CLAUDE.md gains an explicit 'MFA' line
pointing to ADR-0011.
Julien Gautier