Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.ServiceModel/System/ServiceModel/Security/SecurityStateEncoder.cs

@@ -0,0 +1,19 @@
+//------------------------------------------------------------
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+//------------------------------------------------------------
+
+namespace System.ServiceModel.Security
+{
+    // The rationale for making abstract methods protected instead of public is following:
+    // 1. No scenarios for making them public.
+    // 2. Reduction of threat area (other assemblies on the channel can't call these methods other than through reflection).
+    // 3. Reduction of test area (feature is testable only through other high-level features).
+    public abstract class SecurityStateEncoder
+    {
+        protected SecurityStateEncoder() { }
+
+        protected internal abstract byte[] DecodeSecurityState(byte[] data);
+        protected internal abstract byte[] EncodeSecurityState(byte[] data);
+    }
+}
+