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Nested app authentication and Outlook legacy tokens deprecation FAQ

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Exchange user identity tokens and callback tokens are deprecated and will be turned off starting in February 2025. We recommend moving Outlook add-ins that use legacy Exchange tokens to nested app authentication.

General FAQ

What is nested app authentication (NAA)?

Nested app authentication enables single sign-on (SSO) for applications nested inside of supported Microsoft applications such as Outlook. Compared with existing full-trust authentication models, and the on-behalf-of flow, NAA provides better security and greater flexibility in app architecture, enabling the creation of rich, client-driven applications. For more information, see Enable SSO in an Office Add-in using nested app authentication.

What is the timeline for shutting down legacy Exchange online tokens?

Microsoft begins turning off legacy Exchange online tokens in February 2025. From now until February 2025, existing and new tenants will not be affected. We'll provide tooling for administrators to reenable Exchange tokens for tenants and add-ins if those add-ins aren't yet migrated to NAA. See Can I turn legacy tokens back on? for more information.

Date Legacy tokens status
Feb 2025 Legacy tokens turned off for all tenants. Admins can reenable legacy tokens via PowerShell.
Jun 2025 Legacy tokens turned off for all tenants. Admins can no longer reenable legacy tokens via PowerShell and must contact Microsoft for any exception.
Oct 2025 Legacy tokens turned off for all tenants. Exceptions are no longer allowed.

When is NAA generally available for my channel?

The general availability (GA) date for NAA depends on which channel you are using.

Date NAA General Availability (GA)
Oct 2024 NAA is GA in Current Channel.
Nov 2024 NAA will GA in Monthly Enterprise Channel.
Jan 2025 NAA will GA in Semi-Annual Channel.
Jun 2025 NAA will GA in Semi-Annual Extended Channel.

Can I turn legacy tokens back on?

From October 30th through mid-November 2024, we'll roll out new tooling via PowerShell for Microsoft 365 administrators to turn legacy Exchange tokens on or off in your tenant. If you find you need to reenable legacy Exchange tokens, you can use the PowerShell cmdlets to do so. The tooling will also report if any add-ins are using legacy tokens over the last 28 days. We'll update this FAQ with additional information once the tool is available in all tenants.

Outlook add-in migration FAQ

Why is Microsoft making Outlook add-ins migrate?

Switching to Microsoft Graph using Entra ID tokens is a big improvement in security for Outlook and Exchange customers. Entra ID (formerly Azure Active Directory) is a leading cloud-based identity and access management service. Customers can take advantage of zero trust features such as conditional access, MFA requirements, continual token monitoring, real time safety heuristics, and more that aren't available with legacy Exchange tokens. Customers store important business data stored in Exchange, so it's vital that we ensure this data is protected. Migrating the whole Outlook ecosystem to use Entra ID tokens with Microsoft Graph greatly improves security for customer data.

Can I opt out?

We'll provide tooling for administrators to reenable Exchange tokens for tenants and add-ins if those add-ins aren't yet migrated to NAA. See Can I turn legacy tokens back on? for more information. However, in June 2025, legacy Exchange Online tokens will be turned off and you won't be able to turn them back on without a specific exception granted by Microsoft. In October 2025, it won't be possible to turn on legacy Exchange Online tokens and they'll be disabled for all tenants. We'll update this FAQ when more information about this tooling is available.

Does my Outlook add-in have to migrate to NAA?

No. Outlook add-ins don't have to use NAA, although NAA offers the best authentication experience for users and the best security posture for organizations. If add-ins aren't using legacy Exchange tokens, they won't be affected by the deprecation of Exchange tokens. Add-ins using MSAL.js or other SSO methods that rely on Entra ID will continue to work.

How do I know if my Outlook add-in relies on legacy tokens?

We'll provide tooling for administrators that reports the app ID of any add-in that used legacy Exchange online tokens in the last 28 days. We'll provide more information when the tooling is ready in this FAQ. See Can I turn legacy tokens back on? for more information.

To find out whether your add-in uses legacy Exchange user identity tokens and callback tokens, search your code for calls to the following APIs.

  • makeEwsRequestAsync
  • getUserIdentityTokenAsync
  • getCallbackTokenAsync

If your add-in calls any of these APIs, you should adopt NAA and migrate to using Entra ID tokens to access Microsoft Graph instead.

Which Outlook add-ins are in scope?

Many major add-ins are in scope. If your add-in is using EWS or Outlook REST to access Exchange Online resources, it almost certainly needs to migrate off of legacy Outlook tokens to NAA. If your add-in is for Exchange on-premises only (for example, Exchange 2019), it's not affected by this change.

What will happen to my Outlook add-ins if I don't migrate to NAA?

If you don't migrate your Outlook add-ins to NAA, they'll stop working as expected in Exchange Online. When Exchange tokens are turned off (according to the previous table), Exchange Online will block legacy token issuance. Any add-in that uses legacy tokens won't be able to access Exchange online resources. If your add-in only works on-premises or if your add-in is on a deprecation path, you may not need to update. However, most add-ins that access Exchange resources through EWS or Outlook REST must migrate to continue functioning as expected.

How do I migrate my Outlook add-ins to NAA?

To support NAA in your Outlook add-in, please refer to the following documentation and sample.

As an admin, how do I know which add-ins in my org need to be updated?

We'll provide tooling for administrators that reports the app ID of any add-in that used legacy Exchange online tokens in the last 28 days. We'll provide more information when the tooling is ready in this FAQ. See Can I turn legacy tokens back on? for more information.

Add-ins may use the legacy Exchange tokens to get resources from Exchange through the EWS or Outlook REST APIs. Sometimes an add-in requires Exchange resources for some use cases and not others, making it difficult to figure out whether the add-in requires an update. We recommend reaching out to add-in developers and owners to ask them if their add-in code references the following APIs.

  • makeEwsRequestAsync
  • getUserIdentityTokenAsync
  • getCallbackTokenAsync

If you rely on an independent software vendor (ISV) for your add-in, we recommend you contact them as soon as possible to confirm they have a plan and a timeline for moving off legacy Exchange tokens. ISV developers should reach out directly to their Microsoft contacts with questions to ensure they're ready for the end of Exchange legacy tokens. If you rely on a developer within your organization, we recommend you ask them to review the Updates on deprecating legacy Exchange Online tokens for Outlook add-ins blog and ask any questions to the Outlook extensibility PM team on the OfficeDev/office-js GitHub issues site.

How do I keep up with the latest guidance?

We'll update this FAQ as any new information becomes available. We'll share additional guidance moving forward on the Office Add-ins community call and the M365 developer blog. Finally, you can ask questions about NAA and legacy Exchange Online token deprecation on the OfficeDev/office-js GitHub issues site. Please put "NAA" in the title so we can group and prioritize issues.

Developer troubleshooting questions

NAA is not providing SSO and keeps prompting users to sign in

This can occur when NAA is not available in the Outlook client. If on Windows, check that you are using either the Beta Channel, or Current Channel (Preview). You need to join the Microsoft 365 Insider Program to switch to these channels. A good way to check if NAA is available is to check the requirement set using the following code snippet. Office.context.requirements.isSetSupported("NestedAppAuth")

How do I get more debug information from MSAL and NAA?

Use the following code to enable debug information in the msalConfig when you initialize the nestable public client application. This will log additional details to the console.

const msalConfig = {
  auth: {...},
  system: {
    loggerOptions: {
      logLevel: LogLevel.Verbose,
      loggerCallback: (level, message, containsPii) => {
        switch (level) {
          case LogLevel.Error:
            console.error(message);
            return;
          case LogLevel.Info:
            console.info(message);
            return;
          case LogLevel.Verbose:
            console.debug(message);
            return;
          case LogLevel.Warning:
            console.warn(message);
            return;
        }
      },
    }
  }
};

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