Microsoft Entra Connect Sync: Switch to Application-Based Authentication Before April 7, 2027

Microsoft is retiring legacy, password-based authentication for Microsoft Entra Connect Sync. By April 7, 2027, every Connect Sync server must be running version 2.6.84.0 or later and must authenticate to Microsoft Entra ID using Application-Based Authentication (ABA). Servers that miss the deadline will stop synchronizing, which means changes made in on-premises Active Directory will no longer reach the cloud.

What Is Changing, and Why
For years, Entra Connect Sync has signed in to Microsoft Entra ID using a directory synchronization service account protected by a password which leads to the risk of credential theft and misuse. With Application-Based Authentication, Connect Sync authenticates using an application identity in Entra ID backed by a certificate, using the OAuth 2.0 client credentials flow.

The Timeline, and What Happens If You Miss It

• July 2026 — Version 2.6.84.0 released. It is now the minimum version required, and it includes security fixes and improvements to the Application-Based Authentication setup.
• April 7, 2027 — Every Entra Connect Sync server, including staging servers, must run version 2.6.84.0 or later with Application-Based Authentication configured.

If a server is not compliant by April 7, 2027, all synchronization services in Connect Sync will stop until the environment is brought back into a supported configuration.

How to Check Your Environment and Make the Switch

1. Review the current version on every Entra Connect Sync server, including any staging-mode servers, and record which ones are below 2.6.84.0.
2. Upgrade to 2.6.84.0 or later, downloaded from the Microsoft Entra admin center. Confirm prerequisites such as .NET Framework 4.7.2 and TLS 1.2, and upgrade your staging server first so you have a tested fallback.
3. Configure Application-Based Authentication (ABA) by opening the Entra Connect wizard, selecting Additional tasks, and choosing Configure application-based authentication to Microsoft Entra ID.
4. Validate synchronization health. Run a sync cycle, check the Synchronization Service Manager and event logs for errors, confirm PHS, PTA, or federated sign-in still works as intended, and review Microsoft Entra Connect Health for alerts.
   
   

The move to Application-Based Authentication (ABA) is a meaningful security improvement for hybrid identity, but it comes with a hard deadline and a real consequence: if your servers are not ready by April 7, 2027, directory synchronization stops.

Please contact the industry-leading experts at Helient to review your Entra Connect Sync servers, plan the upgrade, and complete the switch to Application-Based Authentication before the April 2027 deadline.