Check out Keith Mayer’s "Step-by-Step" post on "Extending On-Premise Active Directory" to the Cloud with Windows Azure.

http://blogs.technet.com/b/keithmayer/archive/2013/01/20/step-by-step-extending-on-premise-active-directory-to-the-cloud-with-windows-azure-31-days-of-servers-in-the-cloud-part-20-of-31.aspx#.UP1PcWYo6os

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In case you missed any of the series here is a list to all of the articles: http://aka.ms/31azure