The Cloud already is and it has been for a while now a common area for Exchange Administrators where we can integrate our on-premises Exchange with several products offered by Microsoft and other partners. Using Microsoft offers we have Office365, Exchange Online protection and so forth.
In this post the Microsoft Enterprise Mobility Team introduces the Cloud Identity topic including synchronization scenarios and federation.
When you look at managing identity in the cloud, you need to make some initial decisions. Of course, you can always change your approach and expand to add new pieces after the initial setup, but we all know it’s much easier to have an idea of where we want to end up before we start out on a journey.
One of the first things to consider is whether you will be leveraging an on‑premises directory, particularly Active Directory Domain Services (AD DS), or working in a cloud-only environment. For a cloud-only environment, choose Microsoft Azure Active Directory(Azure AD). We’ve already touched on the power of Azure AD, and we will go into more detail later about Azure AD Premium. For now, just keep in mind that Azure AD provides the core identity functions that you need for a cloud-based scenario. You can learn more about how Azure AD and AD DS are similar in the Microsoft TechNet article: Similarities between Active Directory and Azure AD.
Read more at source: http://blogs.technet.com/b/enterprisemobility/archive/2014/05/20/on-boarding-to-the-cloud.aspx