introduce auth interceptor context
diff --git a/src/csharp/Grpc.Core/AsyncAuthInterceptor.cs b/src/csharp/Grpc.Core/AsyncAuthInterceptor.cs
new file mode 100644
index 0000000..5c9ab04
--- /dev/null
+++ b/src/csharp/Grpc.Core/AsyncAuthInterceptor.cs
@@ -0,0 +1,84 @@
+#region Copyright notice and license
+
+// Copyright 2015, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+// * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+using Grpc.Core.Internal;
+using Grpc.Core.Utils;
+
+namespace Grpc.Core
+{
+ /// <summary>
+ /// Asynchronous authentication interceptor for <see cref="CallCredentials"/>.
+ /// </summary>
+ /// <param name="context">The interceptor context.</param>
+ /// <param name="metadata">Metadata to populate with entries that will be added to outgoing call's headers.</param>
+ /// <returns></returns>
+ public delegate Task AsyncAuthInterceptor(AuthInterceptorContext context, Metadata metadata);
+
+ /// <summary>
+ /// Context for an RPC being intercepted by <see cref="AsyncAuthInterceptor"/>.
+ /// </summary>
+ public class AuthInterceptorContext
+ {
+ readonly string serviceUrl;
+ readonly string methodName;
+
+ /// <summary>
+ /// Initializes a new instance of <c>AuthInterceptorContext</c>.
+ /// </summary>
+ public AuthInterceptorContext(string serviceUrl, string methodName)
+ {
+ this.serviceUrl = Preconditions.CheckNotNull(serviceUrl);
+ this.methodName = Preconditions.CheckNotNull(methodName);
+ }
+
+ /// <summary>
+ /// The fully qualified service URL for the RPC being called.
+ /// </summary>
+ public string ServiceUrl
+ {
+ get { return serviceUrl; }
+ }
+
+ /// <summary>
+ /// The method name of the RPC being called.
+ /// </summary>
+ public string MethodName
+ {
+ get { return methodName; }
+ }
+ }
+}