Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Web/Util/ExecutionContextUtil.cs

@@ -0,0 +1,41 @@
+//------------------------------------------------------------------------------
+// <copyright file="ExecutionContextUtil.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>                                                                
+//------------------------------------------------------------------------------
+
+namespace System.Web.Util {
+    using System;
+    using System.Reflection;
+    using System.Security.Permissions;
+    using System.Threading;
+
+    // This class contains utility methods for dealing with security contexts when crossing AppDomain boundaries.
+
+    [SecurityPermission(SecurityAction.LinkDemand, Unrestricted = true)]
+    internal static class ExecutionContextUtil {
+
+        private static readonly ContextCallback s_actionToActionObjShunt = obj => ((Action)obj)();
+        private static readonly ExecutionContext s_dummyDefaultEC = GetDummyDefaultEC();
+
+        [ReflectionPermission(SecurityAction.Assert, MemberAccess = true)]
+        private static ExecutionContext GetDummyDefaultEC() {
+            // The ExecutionContext.PreAllocatedDefault property is special-cased by ExecutionContext to be a blank context and to allow multiple invocation.
+            PropertyInfo propInfo = typeof(ExecutionContext).GetProperty("PreAllocatedDefault", BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static);
+
+            if (propInfo == null) {
+                throw new Exception(SR.GetString(SR.Type_doesnt_have_property, typeof(ExecutionContext).FullName, "PreAllocatedDefault"));
+            }
+
+            return (ExecutionContext) propInfo.GetValue(null, null);
+        }
+
+        // Removes all context associated with the current thread (call context, IPrincipal, etc.) and invokes the provided callback.
+        // The intent of this method is to get any user-provided context off the current thread before crossing an AppDomain boundary,
+        // as the existence of that context could lead to behavioral problems (see DevDiv #205764) or security problems (see DevDiv #206598).
+        internal static void RunInNullExecutionContext(Action callback) {
+            ExecutionContext.Run(s_dummyDefaultEC, s_actionToActionObjShunt, callback);
+        }
+
+    }
+}