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

Contexts/ContextQueryAttrib.cs

@@ -0,0 +1,40 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace NSspi.Contexts
+{
+    /// <summary>
+    /// Defines the types of queries that can be performed with QueryContextAttribute.
+    /// Each query has a different result buffer.
+    /// </summary>
+    public enum ContextQueryAttrib : int
+    {
+        /// <summary>
+        /// Queries the buffer size parameters when performing message functions, such
+        /// as encryption, decryption, signing and signature validation.
+        /// </summary>
+        /// <remarks>
+        /// Results for a query of this type are stored in a Win32 SecPkgContext_Sizes structure.
+        /// </remarks>
+        Sizes = 0,
+
+        /// <summary>
+        /// Queries the context for the name of the user assocated with a security context.
+        /// </summary>
+        /// <remarks>
+        /// Results for a query of this type are stored in a Win32 SecPkgContext_Name structure.
+        /// </remarks>
+        Names = 1,
+
+        /// <summary>
+        /// Queries the name of the authenticating authority for the security context.
+        /// </summary>
+        /// <remarks>
+        /// Results for a query of this type are stored in a Win32 SecPkgContext_Authority structure.
+        /// </remarks>
+        Authority = 6,
+    }
+}