The identity model for Azure Active Directory and all of the connected services has been adapting to customer needs for years. The first approach for most organizations was to use federated identities and it has required a significant investment for availability requirements; if the federation infrastructure is unavailable, nobody signs in. However, this capability offered all of the valuable options like multi-factor authentication, conditional access, and single sign on.
Azure AD Pass-Through Authentication is GA!
Dustin Dortch 