Users who exist in Microsoft Entra ID or LDAP but have no local account
were blocked at the email-first login step because the system required a
local user record before showing SSO options. This adds a domain-based
fallback: when the email is unknown locally, the system checks tenant SSO
configurations for matching allowed_domains and presents SSO-only login
options, enabling the existing JIT provisioning to trigger on callback.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>