Tutorial: Enforce multi-factor authentication for B2B guest users

When collaborating with external B2B guest users, it’s a good idea to protect your apps with multi-factor authentication (MFA) policies. Then external users will need more than just a user name and password to access your resources. In Azure Active Directory (Azure AD), you can accomplish this goal with a Conditional Access policy that requires MFA for access. MFA policies can be enforced at the tenant, app, or individual guest user level, the same way that they're enabled for members of your own organization. The resource tenant is always responsible for Azure AD Multi-Factor Authentication for users, even if the guest user’s organization has Multi-Factor Authentication capabilities.

Example:

Diagram showing a guest user signing into a company's apps.

  1. An admin or employee at Company A invites a guest user to use a cloud or on-premises application that is configured to require MFA for access.
  2. The guest user signs in with their own work, school, or social identity.
  3. The user is asked to complete an MFA challenge.
  4. The user sets up MFA with Company A and chooses their MFA option. The user is allowed access to the application.

Note

Azure AD Multi-Factor Authentication is done at resource tenancy to ensure predictability. When the guest user signs in, they'll see the resource tenant sign-in page displayed in the background, and their own home tenant sign-in page and company logo in the foreground.

In this tutorial, you will:

  • Test the sign-in experience before MFA setup.
  • Create a Conditional Access policy that requires MFA for access to a cloud app in your environment. In this tutorial, we’ll use the Microsoft Azure Management app to illustrate the process.
  • Use the What If tool to simulate MFA sign-in.
  • Test your Conditional Access policy.
  • Clean up the test user and policy.

If you don’t have an Azure subscription, create a free account before you begin.

Prerequisites

To complete the scenario in this tutorial, you need:

  • Access to Azure AD Premium edition, which includes Conditional Access policy capabilities. To enforce MFA, you need to create an Azure AD Conditional Access policy. MFA policies are always enforced at your organization, regardless of whether the partner has MFA capabilities.
  • A valid external email account that you can add to your tenant directory as a guest user and use to sign in. If you don't know how to create a guest account, see Add a B2B guest user in the Azure portal.

Create a test guest user in Azure AD

  1. Sign in to the Azure portal as an Azure AD administrator.

  2. In the Azure portal, select Azure Active Directory.

  3. In the left menu, under Manage, select Users.

  4. Select New user, and then select Invite external user.

    Screenshot showing where to select the new guest user option.

  5. Under Identity, enter the email address of the external user. Optionally, include a name and welcome message.

    Screenshot showing where to enter the guest email.

  6. Select Invite to automatically send the invitation to the guest user. A Successfully invited user message appears.

  7. After you send the invitation, the user account is automatically added to the directory as a guest.

Test the sign-in experience before MFA setup

  1. Use your test user name and password to sign in to your Azure portal.
  2. You should be able to access the Azure portal using only your sign-in credentials. No other authentication is required.
  3. Sign out.

Create a Conditional Access policy that requires MFA

  1. Sign in to your Azure portal as a security administrator or a Conditional Access administrator.

  2. In the Azure portal, select Azure Active Directory.

  3. In the left menu, under Manage, select Security.

  4. Under Protect, select Conditional Access.

  5. On the Conditional Access page, in the toolbar on the top, select New policy.

  6. On the New page, in the Name textbox, type Require MFA for B2B portal access.

  7. In the Assignments section, choose the link under Users and groups.

  8. On the Users and groups page, choose Select users and groups, and then choose Guest or external users. You can assign the policy to different external user types, built-in directory roles, or users and groups.

    Screenshot showing selecting all guest users.

  9. In the Assignments section, choose the link under Cloud apps or actions.

  10. Choose Select apps, and then choose the link under Select.

    Screenshot showing the Cloud apps page and the Select option.

  11. On the Select page, choose Microsoft Azure Management, and then choose Select.

  12. On the New page, in the Access controls section, choose the link under Grant.

  13. On the Grant page, choose Grant access, select the Require multi-factor authentication check box, and then choose Select.

    Screenshot showing the Require multi-factor authentication option.

  14. Under Enable policy, select On.

    Screenshot showing the Enable policy option set to On.

  15. Select Create.

Use the What If option to simulate sign-in

  1. On the Conditional Access | Policies page, select What If.

    Screenshot that highlights where to select the What if option on the Conditional Access - Policies page.

  2. Select the link under User.

  3. In the search box, type the name of your test guest user. Choose the user in the search results, and then choose Select.

    Screenshot showing a guest user selected.

  4. Select the link under Cloud apps, actions, or authentication content. Choose Select apps, and then choose the link under Select.

    Screenshot showing the Microsoft Azure Management app selected.

  5. On the Cloud apps page, in the applications list, choose Microsoft Azure Management, and then choose Select.

  6. Choose What If, and verify that your new policy appears under Evaluation results on the Policies that will apply tab.

    Screenshot showing the results of the What If evaluation.

Test your Conditional Access policy

  1. Use your test user name and password to sign in to your Azure portal.

  2. You should see a request for additional authentication methods. It can take some time for the policy to take effect.

    Screenshot showing the More information required message.

    Note

    You also can configure cross-tenant access settings to trust the MFA from the Azure AD home tenant. This allows external Azure AD users to use the MFA registered in their own tenant rather than register in the resource tenant.

  3. Sign out.

Clean up resources

When no longer needed, remove the test user and the test Conditional Access policy.

  1. Sign in to the Azure portal as an Azure AD administrator.
  2. In the left pane, select Azure Active Directory.
  3. Under Manage, select Users.
  4. Select the test user, and then select Delete user.
  5. In the left pane, select Azure Active Directory.
  6. Under Security, select Conditional Access.
  7. In the Policy Name list, select the context menu (…) for your test policy, and then select Delete. Select Yes to confirm.

Next steps

In this tutorial, you’ve created a Conditional Access policy that requires guest users to use MFA when signing in to one of your cloud apps. To learn more about adding guest users for collaboration, see Add Azure Active Directory B2B collaboration users in the Azure portal.