Added support for querying the context's user name and authority. Still working my way up to EncryptMessage.

Contexts/ContextQueries.cs

@@ -0,0 +1,44 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace NSspi.Contexts
+{
+
+    [StructLayout( LayoutKind.Sequential )]
+    public struct SecPkgContext_Sizes
+    {
+        public int MaxToken;
+        public int MaxSignature;
+        public int BlockSize;
+        public int SecurityTrailer;
+    }
+
+    [StructLayout( LayoutKind.Sequential )]
+    public struct SecPkgContext_String
+    {
+        public IntPtr StringResult;
+    }
+
+
+    public class ContextQueryHandle : SafeHandle
+    {
+        public ContextQueryHandle() :
+            base( IntPtr.Zero, true )
+        {
+        }
+
+        public override bool IsInvalid
+        {
+            get { return base.handle.Equals( IntPtr.Zero ); }
+        }
+
+        protected override bool ReleaseHandle()
+        {
+            return ContextNativeMethods.FreeContextBuffer( base.handle ) == SecurityStatus.OK;
+        }
+    }
+}