Entra Agent ID: The blueprint blast radius

This report analyzes Microsoft Entra's Agent ID (blueprint) architecture and demonstrates that a single blueprint credential can authenticate and impersonate all associated blueprint principals, agent identities, and agent users across tenants. The post details how agent identities are created, the inheritable permissions model, token exchange flows used for impersonation, and how compromise of a blueprint (including third-party blueprints) can produce a large cross-tenant blast radius, increasing the potential impact compared to traditional app registrations.