A Windows Azure AD directory is created automatically for every subscription

Starting today, every Windows Azure subscription is associated with an autocreated directory in Windows Azure Active Directory (AD). By using this enterprise-level identity management service, you can control access to Windows Azure resources.

To accommodate this advancement, every Windows Azure subscription can now host multiple directories. Additionally, Windows Azure SDK will no longer rely on static management certificates but rather on user accounts in Active Directory. Existing Active Directory tenants related to the same user account will be automatically mapped to a single Windows Azure subscription. You can alter these mappings from the Windows Azure Management Portal. Visit the  Windows Azure Management Portal to get started today.