Using AzureAD identities in Azure DevOps organizations backed by Microsoft AccountsAzure DevOps now supports AzureAD (AAD) users accessing organizations that are backed by Microsoft accounts (MSA). 
Just like today, new users are invited to an Azure DevOps organization by entering an email address. 
For organizations that already use AAD identities with Azure DevOps, this feature does not apply. 
For organizations that currently use MSA identities, please note that all existing users can continue to sign in with their MSA identities as they do today. 
Thank you,Justin Marks, Principal PM, Azure DevOps Identity