Letting users authenticate through one corporate identity provider — Google Workspace, Microsoft Entra, Okta — instead of holding a separate password in your product.
For business customers it is often a purchase requirement, not a feature: it is how their IT revokes access the day someone leaves, in one place.
We implement SSO over standard protocols with role mapping from the provider's groups, and we keep an emergency admin path for the day the identity provider itself is unreachable.