Hello @Joe Gilligan,
Thank you for posting your query on Microsoft Q&A.
As you may already know, Microsoft has announced that starting October 15, 2024, MFA will be enforced for sign-ins to the Azure portal , Entra portal and Intune portal as part of Phase 1.
If you are using a third-party MFA provider for second-factor authentication and have configured it through the Conditional Access Custom Controls preview, this will not satisfy the new MFA requirements. You should migrate to the external authentication methods (EAM) preview to continue using your external solution with Microsoft Entra ID.
If you haven't configured your MFA through the external authentication methods preview, please contact your MFA provider and ask them to configure their application according to the requirements outlined in the following documentation:
Microsoft Entra multifactor authentication external method provider reference (Preview)
Once they have made the necessary changes and are satisfied with the flow, you can configure and manage the external authentication method in Microsoft Entra ID by creating an EAM in the admin center.
Manage an external authentication method in Microsoft Entra ID (Preview)
If your third-party MFA provider does not support external authentication methods (EAM) in Microsoft Entra ID, once Microsoft enforces the MFA mandates for the Azure Portal, Entra Portal, and Intune Portal, users will be prompted to register for Azure MFA if an EAM is not configured.
I hope this information is helpful. Please feel free to reach out if you have any further questions.
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Thanks,
Raja Pothuraju.