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diff --git a/src/csharp/Grpc.Auth/OAuth2InterceptorFactory.cs b/src/csharp/Grpc.Auth/OAuth2InterceptorFactory.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.Diagnostics;
+using System.IO;
+using System.Security.Cryptography.X509Certificates;
+using System.Text.RegularExpressions;
+using System.Threading;
+using System.Threading.Tasks;
+
+using Google.Apis.Auth.OAuth2;
+using Google.Apis.Util;
+using Grpc.Core;
+using Grpc.Core.Utils;
+
+namespace Grpc.Auth
+{
+    public static class OAuth2InterceptorFactory
+    {
+        /// <summary>
+        /// Creates OAuth2 interceptor.
+        /// </summary>
+        public static HeaderInterceptorDelegate Create(GoogleCredential googleCredential)
+        {
+            var interceptor = new OAuth2Interceptor(googleCredential.InternalCredential, SystemClock.Default);
+            return new HeaderInterceptorDelegate(interceptor.InterceptHeaders);
+        }
+
+        /// <summary>
+        /// Injects OAuth2 authorization header into initial metadata (= request headers).
+        /// </summary>
+        private class OAuth2Interceptor
+        {
+            private const string AuthorizationHeader = "Authorization";
+            private const string Schema = "Bearer";
+
+            private ServiceCredential credential;
+            private IClock clock;
+
+            public OAuth2Interceptor(ServiceCredential credential, IClock clock)
+            {
+                this.credential = credential;
+                this.clock = clock;
+            }
+
+            /// <summary>
+            /// Gets access token and requests refreshing it if is going to expire soon.
+            /// </summary>
+            /// <param name="cancellationToken"></param>
+            /// <returns></returns>
+            public string GetAccessToken(CancellationToken cancellationToken)
+            {
+                if (credential.Token == null || credential.Token.IsExpired(clock))
+                {
+                    // TODO(jtattermusch): Parallel requests will spawn multiple requests to refresh the token once the token expires.
+                    // TODO(jtattermusch): Rethink synchronous wait to obtain the result.
+                    if (!credential.RequestAccessTokenAsync(cancellationToken).Result)
+                    {
+                        throw new InvalidOperationException("The access token has expired but we can't refresh it");
+                    }
+                }
+                return credential.Token.AccessToken;
+            }
+
+            public void InterceptHeaders(Metadata.Builder headerBuilder)
+            {
+                var accessToken = GetAccessToken(CancellationToken.None);
+                headerBuilder.Add(new Metadata.MetadataEntry(AuthorizationHeader, Schema + " " + accessToken));
+            }
+        }
+    }
+}