Microsoft Expands Multi-Factor Authentication Methods to Companion Apps

Introducing Authenticator Lite

Without too much fuss, Microsoft introduced the preview of a new “surface” (way) for users to complete multi-factor authentication (MFA) challenges. The new method is a companion app for the Microsoft Authenticator app and is covered by Microsoft 365 roadmap item 122289 and is slated for roll-out in May 2023.

Azure AD already covers a variety of methods to satisfy MFA challenges. The methods are categorized from weak to strong in terms of their ability to resist attacks and conditional access policies can insist that a connection uses a certain strength of MFA response before it is accepted. “Authenticator lite” is rated as strong as the Authenticator app because it’s basically code taken from Authenticator and built into other Microsoft apps. In addition, Authenticator lite only supports push notifications with number matching and one-time codes, which are less likely to provoke MFA fatigue than the traditional “click here to approve” response.

Outlook Mobile Leads the Way

Outlook mobile (iOS 4.2309.0, Android 4.2308.0, or higher versions) is the first Microsoft 365 app to pick up the Authenticator Lite code. Some might ask why Microsoft choose Outlook as the test case. I think it’s because Outlook is likely the most heavily used mobile client. The last time Microsoft gave a number for Outlook mobile (April 2019), they reported that Outlook for iOS and Android had more than 100 million users. At that time, Office 365 reached 180 million monthly active users. Now Office 365 is up around 400 million monthly active users. Assuming Outlook mobile has kept pace, it has around 220 million monthly active users.

Building MFA responses into the most popular mobile client is a great way of making MFA easier for organizations to deploy. Microsoft wants customers to deploy MFA. They also want customers to use strong MFA responses and move away from methods like SMS text-based responses. The recent introduction of the Azure AD system-preferred authentication policy to force Azure AD to select the strongest available authentication method for a user when it issues a challenge is a pointer to the future. Who needs to resort to an SMS response when you can respond to a number challenge within Outlook? It makes absolute sense.

Update the Azure AD Authentication Methods Policy

If you’re interested in trying Authenticator Lite with Outlook mobile, the steps to make everything happen are covered in a Microsoft article. In summary:

First, use a Graph API PATCH request to update the Azure AD Authentication Methods Policy to update the companionAppAllowedState setting from disabled (the default) to enabled. The easiest way to do this is with the Graph Explorer (make sure to sign in with an administrator account because you’ll need to consent to the Policy.ReadWrite.AuthenticationMethod permission to update the policy. The relevant lines for the policy in my tenant look like those shown in Figure 1. The state is enabled and the policy is targeted at a group of users with an identifier of “all_users.” This is a special identifier that instructs Azure AD to apply the policy setting to all tenant users. If you want to limit the policy to a specific set of users, create a security group with those users as members and update the authentication methods policy with the group identifier.

Checking the settings of the Azure AD Authentication Methods policy

Authenticator Lite
Figure 1: Checking the settings of the Azure AD Authentication Methods policy

The updated policy might take a little time to become effective and people can respond to MFA challenges from Outlook. Only accounts enabled to use the Authenticator app (with the mode set to Push or Any) to respond to MFA challenges can use Authenticator Lite within Outlook, and responses are limited to number matching or one-time codes. It’s important to realize that if the Microsoft Authenticator app is present on a device, Outlook won’t attempt to use Authenticator Lite and instead refers all authentication challenges to the full Authenticator app.

It’s also important to realize that the code incorporated into Outlook supports fewer options than the full Authenticator app. For instance, it doesn’t support Self-Service Password Reset (SSPR). The Authenticator app is a more appropriate option for users who need functionality like handling MFA responses for other cloud services like Twitter and GitHub.

MFA Responses for the Masses

I like any action that reduces the friction of MFA deployment and operation for both organizations and users. Authenticator Lite falls into this category. Although I won’t use the new capability because I need the power of the full Authenticator app, I think that Authenticator Lite will meet the needs of most Microsoft 365 users when it comes to responding to MFA challenges.

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