Index: Src/GoogleApis.Auth.WP81/OAuth2/GoogleWebAuthorizationBroker.cs
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+/*
+Copyright 2014 Google Inc
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using Windows.Storage;
+
+using Google.Apis.Auth.OAuth2.Flows;
+using Google.Apis.Util.Store;
+
+namespace Google.Apis.Auth.OAuth2
+{
+    /// <summary>A helper utility to manage the authorization code flow.</summary>
+    public class GoogleWebAuthorizationBroker
+    {
+        /// <summary>Asynchronously authorizes the specified user.</summary>
+        /// <remarks>
+        /// It uses <see cref="Google.Apis.Util.Store.PasswordVaultDataStore"/> as the flow's data store by default.
+        /// </remarks>
+        /// <param name="clientSecretsUri">The client secrets URI.</param>
+        /// <param name="scopes">
+        /// The scopes which indicate the Google API access your application is requesting.
+        /// </param>
+        /// <param name="user">The user to authorize.</param>
+        /// <param name="taskCancellationToken">Cancellation token to cancel an operation.</param>
+        /// <returns>User credential.</returns>
+        public static async Task<UserCredential> AuthorizeAsync(Uri clientSecretsUri, IEnumerable<string> scopes,
+            string user, CancellationToken taskCancellationToken)
+        {
+            var clientSecrets = await LoadClientSecrets(clientSecretsUri).ConfigureAwait(false);
+            return await AuthorizeAsync(clientSecrets, scopes, user, taskCancellationToken).ConfigureAwait(false);
+        }
+
+        /// <summary>
+        /// Asynchronously reauthorizes the user. This method should be called if the users want to authorize after 
+        /// they revoked the token.
+        /// </summary>
+        /// <param name="userCredential">The current user credential. Its <see cref="UserCredential.Token"/> will be
+        /// updated. </param>
+        /// <param name="taskCancellationToken">Cancellation token to cancel an operation.</param>
+        public static async Task ReauthorizeAsync(UserCredential userCredential,
+            CancellationToken taskCancellationToken)
+        {
+            var installedApp = new AuthorizationCodeWPInstalledApp(userCredential.Flow);
+            // Create an authorization code installed app instance and authorize the user.
+            UserCredential newUserCredential = await installedApp.AuthorizeAsync(
+                userCredential.UserId, taskCancellationToken).ConfigureAwait(false);
+            userCredential.Token = newUserCredential.Token;
+        }
+
+        /// <summary>Asynchronously authorizes the specified user.</summary>
+        /// <remarks>
+        /// It uses <see cref="Google.Apis.Util.Store.PasswordVaultDataStore"/> as the flow's data store by default.
+        /// </remarks>
+        /// <param name="clientSecrets">The client secrets URI.</param>
+        /// <param name="scopes">
+        /// The scopes which indicate the Google API access your application is requesting.
+        /// </param>
+        /// <param name="user">The user to authorize.</param>
+        /// <param name="taskCancellationToken">Cancellation token to cancel an operation.</param>
+        /// <returns>User credential.</returns>
+        private static async Task<UserCredential> AuthorizeAsync(ClientSecrets clientSecrets,
+            IEnumerable<string> scopes, string user, CancellationToken taskCancellationToken)
+        {
+            var initializer = new GoogleAuthorizationCodeFlow.Initializer
+            {
+                ClientSecrets = clientSecrets,
+                Scopes = scopes,
+                DataStore = new PasswordVaultDataStore()
+            };
+
+            var installedApp = new AuthorizationCodeWPInstalledApp(new GoogleAuthorizationCodeFlow(initializer));
+            return await installedApp.AuthorizeAsync(user, taskCancellationToken).ConfigureAwait(false);
+        }
+
+        /// <summary>Loads the client secrets from the given URI.</summary>
+        /// <param name="clientSecretsUri">The client secrets URI.</param>
+        /// <returns>Client secrets.</returns>
+        private static async Task<ClientSecrets> LoadClientSecrets(Uri clientSecretsUri)
+        {
+            var file = await StorageFile.GetFileFromApplicationUriAsync(clientSecretsUri);
+            var content = await FileIO.ReadTextAsync(file);
+
+            using (var stream = new MemoryStream(Encoding.UTF8.GetBytes(content)))
+            {
+                return GoogleClientSecrets.Load(stream).Secrets;
+            }
+        }
+    }
+}