Explore application objects and service principals

  • 3 minutes

When you've completed the app registration, you have a globally unique instance of the app (the application object) that lives within your home tenant or directory. You also have a globally unique ID for your app (the app/client ID). In the portal, you can then add secrets or certificates and scopes to make your app work, customize the branding of your app in the sign-in dialog, and more.

If you register an application in the portal, an application object and a service principal object are automatically created in your home tenant. If you register/create an application using the Microsoft Graph APIs, creating the service principal object is a separate step.

Application object

A Microsoft Entra application is defined by its one and only application object, which resides in the Microsoft Entra tenant where the application was registered (known as the application's "home" tenant). An application object is used as a template or blueprint to create one or more service principal objects. A service principal is created in every tenant where the application is used. Similar to a class in object-oriented programming, the application object has some static properties that are applied to all the created service principals (or application instances).

The application object describes three aspects of an application:

  • How the service can issue tokens in order to access the application
  • The resources that the application might need to access
  • The actions that the application can take

The application object may include (but not limited to) any of the following:

  • Name, logo, and publisher
  • Redirect URIs
  • Secrets (symmetric and/or asymmetric keys used to authenticate the application)
  • API dependencies (OAuth)
  • Published APIs/resources/scopes (OAuth)
  • App roles
  • Single sign-on (SSO) metadata and configuration
  • User provisioning metadata and configuration
  • Proxy metadata and configuration

Service principal object

To access resources that are secured by a Microsoft Entra tenant, the entity that requires access must be represented by a security principal. This requirement is true for both users (user principal) and applications (service principal). The security principal defines the access policy and permissions for the user/application in the Microsoft Entra tenant. This enables core features such as authentication of the user/application during sign-in, and authorization during resource access. The types of service principal:

  • Application - This type of service principal is the local representation, or application instance, of a global application object in a single tenant or directory. In this case, a service principal is a concrete instance created from the application object and inherits certain properties from that application object.
  • Managed identity - This type of service principal is used to represent a managed identity. Managed identities eliminate the need for developers to manage credentials. Managed identities provide an identity for applications to use when connecting to resources that support Microsoft Entra ID authentication.
  • Legacy - This type of service principal represents a legacy app, which is an app created before app registrations were introduced or an app created through legacy experiences. A legacy service principal can have credentials, service principal names, reply URLs, and other properties that an authorized user can edit, but doesn't have an associated app registration.

The service principal can include:

  • A reference back to an application object through the application ID property
  • Records of local user and group application-role assignments
  • Records of local user and admin permissions granted to the application
  • Records of local policies including Conditional Access policy
  • Records of alternate local settings for an application

Relationship between application objects and service principals

The application object is the global representation of your application for use across all tenants, and the service principal is the local representation for use in a specific tenant. The application object serves as the template from which common and default properties are derived for use in creating corresponding service principal objects. An application object has:

  • A one-to-one relationship with the software application, and
  • A one-to-many relationship with its corresponding service principal object(s)

A service principal must be created in each tenant where the application is used, enabling it to establish an identity for sign-in and/or access to resources being secured by the tenant. A single-tenant application has only one service principal (in its home tenant), created and consented for use during application registration. A multitenant application also has a service principal created in each tenant where a user from that tenant has consented to its use.