Implements more BackOfficeController and AuthenticationController, some web security and more, gets the back office UI almost rendering

src/Umbraco.Web.Common/Extensions/HttpContextExtensions.cs

@@ -0,0 +1,37 @@
+using Microsoft.AspNetCore.Http;
+using System;
+using System.Collections.Generic;
+using System.Security.Claims;
+using System.Security.Principal;
+using System.Text;
+using Umbraco.Core.BackOffice;
+
+namespace Umbraco.Extensions
+{
+    public static class HttpContextExtensions
+    {
+        public static void SetPrincipalForRequest(this HttpContext context, ClaimsPrincipal principal)
+        {
+            context.User = principal;
+        }
+
+        /// <summary>
+        /// This will return the current back office identity.
+        /// </summary>
+        /// <param name="http"></param>        
+        /// <returns>
+        /// Returns the current back office identity if an admin is authenticated otherwise null
+        /// </returns>
+        public static UmbracoBackOfficeIdentity GetCurrentIdentity(this HttpContext http)
+        {
+            if (http == null) throw new ArgumentNullException(nameof(http));
+            if (http.User == null) return null; //there's no user at all so no identity
+
+            // If it's already a UmbracoBackOfficeIdentity
+            var backOfficeIdentity = http.User.GetUmbracoIdentity();
+            if (backOfficeIdentity != null) return backOfficeIdentity;
+
+            return null;
+        }
+    }
+}