Microsoft Entra ID is no longer used only to authenticate employees and other human users. Modern cloud environments depend heavily on applications, automated services, Azure resources, integrations, and increasingly autonomous agents. Each of these non-human actors may need an identity that allows it to authenticate, obtain tokens, and access resources according to defined permissions. Understanding how these identities are represented is therefore essential for both identity administration and security.
The architecture can initially seem complicated because several identity concepts overlap. Application objects, service principals, managed identities, and newer agent-related identities have different purposes, but many ultimately rely on service principal objects within the directory. A practical way to understand the landscape is to examine the main categories, how they are created, and where their security boundaries exist.
The Service Principal Foundation Behind Workload Identities
The term workload identity describes non-human identities that allow applications, services, automation workloads, cloud resources, and other software-based actors to authenticate without direct human interaction. In Entra ID, the service principal is the central object behind many of these identities. Microsoft Graph represents service principals as a flexible directory resource capable of carrying permissions, credentials, ownership, application roles, group memberships, and other security-related information.
This makes service principals the key to understanding Entra workload identity types. Microsoft documentation identifies five primary logical values for the servicePrincipalType property: Application, ManagedIdentity, Legacy, SocialIdp, and ServiceIdentity. These categories do not all behave identically, even though they share the service principal foundation.
The distinction matters because administrators cannot safely assume that every service principal has the same authentication method or lifecycle. Some are created from application registrations, some are tied directly to Azure resources, while others represent specialized or older integration models. The underlying object may look familiar, but its origin and behavior determine how it should be managed.
Application Identities and Their Tenant-Specific Service Principals
Applications are one of the most common categories of Entra workload identity types. An application object acts as the global definition or blueprint of an application. It contains information such as the application identifier, redirect URIs, required API permissions, and credentials. The corresponding service principal represents that application inside a particular Entra tenant and is the object that participates directly in authorization and access decisions.
This distinction is especially important for organizations using third-party SaaS applications or developing their own internal applications. A single application can have service principal instances in multiple tenants. Each tenant’s service principal can have different permissions and consent settings, even though the underlying application identifier remains associated with the same application definition.
Application-backed service principals generally fall into three practical groups:
- Microsoft first-party applications that provide services such as Microsoft Graph, Exchange Online, SharePoint, or other Microsoft cloud capabilities.
- Organization-owned applications registered by administrators or developers through the App Registrations experience.
- Third-party or gallery applications, including SaaS platforms integrated through the Microsoft Entra application gallery.
For security teams, the service principal is particularly important because it becomes the runtime identity that receives permissions and participates in authentication. OAuth permission grants, app role assignments, tenant-specific consent, and service-principal credentials can all affect what the application is capable of doing. Consequently, an application that appears harmless at the application-registration level may still represent a significant access path once its service principal has been granted powerful permissions.
The relationship also creates an important administrative consideration. Credentials added to an application object can affect service principals associated with that application across consenting tenants, whereas credentials attached directly to a service principal are scoped to that tenant. This distinction makes ownership, credential management, and consent review essential parts of application identity governance.
Managed Identities: Azure-Controlled Authentication Without Stored Secrets
Managed identities provide another major category of workload identities in Entra ID. Their primary purpose is to remove much of the manual credential-management burden associated with applications and automated workloads. Instead of developers storing a client secret or certificate and periodically rotating it, Azure manages the identity and its authentication mechanism as part of the platform.
There are two main forms: system-assigned and user-assigned managed identities. A system-assigned identity is created alongside a supported Azure resource and has a tightly coupled one-to-one lifecycle. When the resource is deleted, its identity is deleted as well. A user-assigned managed identity is an independent Azure resource that can be associated with multiple supported resources. This provides greater flexibility but also creates a broader lifecycle and permission-management responsibility.
Managed identities are represented in Entra ID through service principals whose servicePrincipalType is ManagedIdentity. Unlike application-backed identities, they are not associated with a conventional application registration and do not depend on SAML, OpenID Connect, or password-based single sign-on configurations. Azure handles token acquisition through platform-controlled identity endpoints.
That design substantially reduces exposure to common secret-management problems, but it does not eliminate identity risk. The resource hosting a managed identity becomes an important security boundary. Code executing on a compromised virtual machine, application service, or other supported resource may be able to request a token for an identity available to that resource. If the identity has excessive permissions, an attacker who gains code execution may therefore turn access to the resource into access to additional Azure services.
User-assigned identities require particular attention because they can be attached to multiple resources. This flexibility can simplify architecture, but it can also increase the potential impact of a compromised resource. Least-privilege permissions and careful assignment of identities to workloads remain fundamental safeguards.
Legacy, Social Identity, and Emerging ServiceIdentity Types
The remaining service principal categories are less common in many ordinary deployments but are still relevant when examining an Entra tenant comprehensively. Legacy identities generally reflect older authentication or service models that continue to exist for compatibility. SocialIdp identities are associated with social identity providers and federation scenarios rather than conventional internal application workloads.
ServiceIdentity is particularly noteworthy because Microsoft has introduced it as the service principal type associated with newer agent identity capabilities. This reflects an important evolution in Entra ID: software is increasingly capable of acting autonomously, making decisions and interacting with services on behalf of users or organizations.
Agent identities build upon existing identity infrastructure rather than existing as an entirely separate authentication universe. Microsoft describes specialized agent identity objects as service-principal-based objects, which means established concepts such as permissions, ownership, credentials, logging, and authorization remain highly relevant.
This inheritance has practical consequences. Reusing established identity infrastructure can provide compatibility with existing APIs and security controls, but it can also make authorization boundaries more complicated. A permission intended for a specialized identity type must be carefully constrained so that it cannot unintentionally provide authority over unrelated service principals.
Applying Least Privilege Across the Identity Lifecycle
Regardless of the identity category, security begins with understanding what an identity can access and why it needs that access. Organizations should inventory service principals, identify their owners, examine credentials, review granted permissions, and remove identities that are no longer required.
Credential hygiene is equally important. Secrets and certificates associated with application identities should have controlled lifecycles, while managed identities should be assigned only to resources that genuinely require them. Permissions should be limited to the smallest practical scope rather than granting broad directory or resource access for convenience.
Monitoring also matters because non-human identities often operate continuously and may generate activity without a user sitting at a keyboard. Sign-in logs, audit records, application consent changes, credential modifications, and unusual permission assignments can provide useful signals when investigating suspicious activity.
Finally, identity governance should account for the difference between an identity’s logical category and its actual privileges. A service principal labeled as an application or managed identity is not inherently safe or dangerous—the permissions attached to it determine much of its effective security impact. This is why inventory, ownership, privilege review, and lifecycle controls should work together rather than being treated as separate administrative tasks.
Final Analysis
The main identity categories in Entra ID are easier to understand when viewed through their underlying architecture. Application-backed service principals provide runtime identities for registered, Microsoft, and third-party applications. Managed identities connect Azure resources to authentication without requiring developers to maintain conventional secrets. Legacy and social identity types support specialized scenarios, while newer service-oriented identity models extend the platform toward autonomous software and agents.
The most useful lesson is that identity type alone does not determine risk. Administrators need to understand where an identity originated, how it authenticates, what permissions it possesses, who controls it, and which resources depend on it. With that context, Entra ID’s seemingly complex identity landscape becomes much more manageable—and organizations can make more informed decisions about access, monitoring, and lifecycle management.