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diff --git a/src/csharp/Grpc.Core/CallCredentials.cs b/src/csharp/Grpc.Core/CallCredentials.cs
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+++ b/src/csharp/Grpc.Core/CallCredentials.cs
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+#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>
+    /// Client-side call credentials. Provide authorization with per-call granularity.
+    /// </summary>
+    public abstract class CallCredentials
+    {
+        /// <summary>
+        /// Composes multiple multiple <c>CallCredentials</c> objects into
+        /// a single <c>CallCredentials</c> object.
+        /// </summary>
+        /// <param name="credentials">credentials to compose</param>
+        /// <returns>The new <c>CompositeCallCredentials</c></returns>
+        public static CallCredentials Compose(params CallCredentials[] credentials)
+        {
+            return new CompositeCallCredentials(credentials);
+        }
+
+        /// <summary>
+        /// Creates native object for the credentials.
+        /// </summary>
+        /// <returns>The native credentials.</returns>
+        internal abstract CredentialsSafeHandle ToNativeCredentials();
+    }
+
+    /// <summary>
+    /// Asynchronous authentication interceptor for <see cref="MetadataCredentials"/>.
+    /// </summary>
+    /// <param name="authUri">URL of a service to which current remote call needs to authenticate</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(string authUri, Metadata metadata);
+
+    /// <summary>
+    /// Client-side credentials that delegate metadata based auth to an interceptor.
+    /// The interceptor is automatically invoked for each remote call that uses <c>MetadataCredentials.</c>
+    /// </summary>
+    public class MetadataCredentials : CallCredentials
+    {
+        readonly AsyncAuthInterceptor interceptor;
+
+        /// <summary>
+        /// Initializes a new instance of <c>MetadataCredentials</c> class.
+        /// </summary>
+        /// <param name="interceptor">authentication interceptor</param>
+        public MetadataCredentials(AsyncAuthInterceptor interceptor)
+        {
+            this.interceptor = interceptor;
+        }
+
+        internal override CredentialsSafeHandle ToNativeCredentials()
+        {
+            NativeMetadataCredentialsPlugin plugin = new NativeMetadataCredentialsPlugin(interceptor);
+            return plugin.Credentials;
+        }
+    }
+
+    /// <summary>
+    /// Credentials that allow composing multiple credentials objects into one <see cref="CallCredentials"/> object.
+    /// </summary>
+    internal sealed class CompositeCallCredentials : CallCredentials
+    {
+        readonly List<CallCredentials> credentials;
+
+        /// <summary>
+        /// Initializes a new instance of <c>CompositeCallCredentials</c> class.
+        /// The resulting credentials object will be composite of all the credentials specified as parameters.
+        /// </summary>
+        /// <param name="credentials">credentials to compose</param>
+        public CompositeCallCredentials(params CallCredentials[] credentials)
+        {
+            Preconditions.CheckArgument(credentials.Length >= 2, "Composite credentials object can only be created from 2 or more credentials.");
+            this.credentials = new List<CallCredentials>(credentials);
+        }
+
+        internal override CredentialsSafeHandle ToNativeCredentials()
+        {
+            return ToNativeRecursive(0);
+        }
+
+        // Recursive descent makes managing lifetime of intermediate CredentialSafeHandle instances easier.
+        // In practice, we won't usually see composites from more than two credentials anyway.
+        private CredentialsSafeHandle ToNativeRecursive(int startIndex)
+        {
+            if (startIndex == credentials.Count - 1)
+            {
+                return credentials[startIndex].ToNativeCredentials();
+            }
+
+            using (var cred1 = credentials[startIndex].ToNativeCredentials())
+            using (var cred2 = ToNativeRecursive(startIndex + 1))
+            {
+                var nativeComposite = CredentialsSafeHandle.CreateComposite(cred1, cred2);
+                if (nativeComposite.IsInvalid)
+                {
+                    throw new ArgumentException("Error creating native composite credentials. Likely, this is because you are trying to compose incompatible credentials.");
+                }
+                return nativeComposite;
+            }
+        }
+    }
+}