Service Principal ID
What is Service Principal?
A Service Principal is a security identity in Azure Active Directory (Entra ID) that represents an application or service, allowing it to log in and access Azure resources — just like a user, but for apps or automation.
What is a Service Principal ID?
The Service Principal ID is the unique identifier (GUID) assigned to the Service Principal object in Azure Active Directory (Entra ID).
Application ID
Also known as: App ID
What it is Application ID:
A globally unique identifier for the Azure AD Application registration.
Scope: Refers to the actual application definition in Azure AD.
Example use: When configuring authentication for apps (e.g., OAuth2, OpenID), you often use the Application ID.
Client ID
Also known as: App ID (again!)
What it is Client ID
Client ID: This is actually the same as the Application ID in most contexts.
Why it’s called “Client ID”: In OAuth2 terminology, the application (a “client”) gets a Client ID and Client Secret.
Example use: When an app authenticates using OAuth2, it presents the Client ID and secret.
Quick Comparison Table:
| Term | Alias | Refers To | Example Use |
|---|---|---|---|
| Application ID | Client ID | App registration in Azure AD | App registration, API authentication |
| Client ID | Application ID | OAuth2 client ID for authentication | Login with Azure AD |
| Service Principal ID | Object ID | Azure AD identity for app in a tenant | Assign RBAC roles, permissions |
Key Properties
| Property | Description |
|---|---|
| Client ID | The App (Application) ID of the Service Principal |
| Tenant ID | The Azure AD tenant where the identity resides |
| Object ID | The unique ID of the Service Principal itself |
| Client Secret | Password-like credential used for authentication |
Breakdown of IDs:
So: Client ID == Application ID
| Name | Also Called As | What it Represents |
|---|---|---|
| Application ID | App ID / Client ID | The registered app in Azure AD |
| Service Principal ID | Object ID | The specific identity of the app in the tenant |
| Tenant ID | — | The Azure AD directory (organization) |