Some refactoring to decouple web based assemblies from Umbraco.Core and move whatever we can to Umbraco.Web where web based assemblies are used. Decouples System.Drawing entirely from Umbraco.Core and removes the Active Directory dependency from Umbraco.core.

src/Umbraco.Web/Security/BackOfficeUserManagerMarker.cs

@@ -0,0 +1,27 @@
+using System;
+using Microsoft.AspNet.Identity.Owin;
+using Microsoft.Owin;
+using Umbraco.Core.Models.Identity;
+using Umbraco.Core.Security;
+
+namespace Umbraco.Web.Security
+{
+    /// <summary>
+    /// This class is only here due to the fact that IOwinContext Get / Set only work in generics, if they worked
+    /// with regular 'object' then we wouldn't have to use this work around but because of that we have to use this
+    /// class to resolve the 'real' type of the registered user manager
+    /// </summary>
+    /// <typeparam name="TManager"></typeparam>
+    /// <typeparam name="TUser"></typeparam>
+    internal class BackOfficeUserManagerMarker<TManager, TUser> : IBackOfficeUserManagerMarker
+        where TManager : BackOfficeUserManager<TUser>
+        where TUser : BackOfficeIdentityUser
+    {
+        public BackOfficeUserManager<BackOfficeIdentityUser> GetManager(IOwinContext owin)
+        {
+            var mgr = owin.Get<TManager>() as BackOfficeUserManager<BackOfficeIdentityUser>;
+            if (mgr == null) throw new InvalidOperationException("Could not cast the registered back office user of type " + typeof(TManager) + " to " + typeof(BackOfficeUserManager<BackOfficeIdentityUser>));
+            return mgr;
+        }
+    }
+}