When you adding a user to Azure Active Directory via the old portal you see this screen:
It allows you to add a user with an existing microsoft account.
I need to import many users with existing microsoft accounts. I'm planning on writing a powershell script to achive that.
How do I add an exising microsoft account to Azure AD with a powershell script?
New-AzureADUser complains that "userPrincipalName" is invalid, as can be seen in this question. Is there another way?