Microsoft has announced that starting March 2026, Entra ID will no longer support service principal-less authentication behavior. This change aims to enhance security by ensuring that all applications authenticate using a service principal, thereby providing better governance and control over application access.
Table of Contents
What is Service Principal-Less Authentication?
Service principal-less authentication refers to scenarios where multitenant applications access resources in a tenant without having an enterprise application (service principal) registered in that tenant. In such cases, tokens are issued without permissions and without an object identifier (object ID), which can pose security risks if resource applications perform incomplete validations.
Why is Microsoft Retiring This?
The retirement of service principal-less authentication is part of Microsoft’s “Security by default” initiative. By enforcing the requirement that applications must be registered in every tenant where they authenticate, tenant administrators gain better governance of all access, including the ability to write conditional access policies for these applications. This change minimizes the risk of unauthorized access and potential exploitation in third-party resources outside Microsoft’s control.
Explanation
- Multitenant Applications: These are applications designed to be used by users from multiple different Microsoft Entra ID tenants (organizations). Imagine a SaaS application like a project management tool where different companies can sign up and use it. Each company has its own Entra ID tenant.
- Resource Tenant: This is the specific Microsoft Entra ID tenant that contains the resources the multitenant application wants to access. For example, if the project management tool wants to read user profiles or files within a particular company’s Microsoft 365 environment, that company’s Entra ID is the resource tenant.
- Enterprise Application Registration: When a multitenant application needs to access resources in a specific tenant (the resource tenant), a representation of that application needs to be created within that tenant. This representation is called an “enterprise application registration.” It’s like saying, “This multitenant app is allowed to operate within our organization.” This registration defines things like permissions the application has and how users in that tenant can interact with it.
“Microsoft Entra ID will block authentication for multitenant applications that don’t have an enterprise application registration in the resource tenant.”
Here’s what this means in simpler terms:
- A Multitenant App Wants Access: Imagine a project management app (the multitenant application) wants to access some files stored in “Company A’s” Microsoft 365 (Company A’s Entra ID is the resource tenant).
- The Check: When a user from Company A tries to log into the project management app and it attempts to access those files, Microsoft Entra ID in Company A’s tenant will check if there’s an “enterprise application registration” for that specific project management app within their tenant.
- No Registration, No Entry: If there’s no enterprise application registration for the project management app in Company A’s tenant, Microsoft Entra ID will block the authentication. This means the user from Company A won’t be able to log in to the project management app and the app won’t be able to access resources in Company A’s tenant.
Timeline
- Announcement Date: March 26, 2025
- Enforcement Date: March 31, 2026
All applications making service principal-less authentication requests in a tenant will be impacted, and the login flow will fail unless action is taken by March 31, 2026.
How to Prepare
- Identify Affected Applications:
- Navigate to the Microsoft Entra admin center.
- Go to Identity > Monitoring & health > Sign-in logs.
- Filter by Service principal ID with the value 00000000-0000-0000-0000-000000000000.
- Review the sign-in logs to identify applications using service principal-less authentication.
- Create Enterprise Applications:
- For each identified application, create an enterprise application in the resource tenant using the Client Application ID obtained from the sign-in logs.
- Verify Tokens:
- Ensure that tokens issued to the application are no longer service principal-less by checking that the Service principal ID in the sign-in logs appears with a unique alphanumeric GUID (e.g., aaaaaaaa-bbbb-cccc-1111-222222222222).
Current Workflow (Before March 2026)
There are two main types of app authentication flows:
With Enterprise App Registration ✅ Supported
Applications (multitenant or single-tenant) authenticate using an enterprise app registration created in the tenant.
Without Enterprise App Registration (SP-less) ✅ Still supported until March 31, 2026
Certain Microsoft applications authenticate without needing an enterprise app registration in the tenant.
Visual Flow Diagram
Future Workflow (After March 31, 2026)
With Service Principal (Only one flow remains)
- 🔒 Authentication requires:
- App registration in Microsoft Entra ID.
- Creation of a service principal in the tenant.
- ✅ Admin consent may be needed (depending on permissions) to register in the tenant.
Visual Flow Diagram
Preparation Tips
- Ensure users can register applications or grant consent.
- If the app isn’t publisher verified, the consent prompt for the app shows unverified. No publisher domain-related information appears.
- If the app is publisher verified, the app consent prompt shows a blue verified badge.
- Review conditional access policies that might block new SP creation.
- Audit existing usage applications.
- Inform developers and IT admins using scripts/tools to test SP-based flows before March 2026.
Additional Resources
- Retire Service Principal-Less Authentication – Microsoft Learn
- Application and Service Principal Objects in Microsoft Entra ID
- Securing Service Principals in Microsoft Entra ID
By proactively identifying and updating applications to use registered service principals, organizations can ensure a smooth transition ahead of the March 2026 deadline and maintain secure access to their resources.
