Identity by Design treats identity as a security control plane from the first decision, not the last. Authentication, authorisation, governance, lifecycle, machine identity, agent identity, and the signals between them are designed together — against the threat model you actually face, the operational reality you actually have, and the business outcomes you actually need. The platform choices come second. The integration list comes second. The intent comes first, and the intent is yours.
Architecture is the discipline that delivers on the promise. Where design is the intent — the principles, the outcomes, the security posture you are aiming at — architecture is how those intentions are composed into a coherent control plane delivery teams can build, operations can run, and the next change does not break. We use the words together deliberately: one without the other produces either a wishlist or a wiring diagram.