Issue 471: Support WP8.1

Src/GoogleApis.Auth.WP81/OAuth2/GoogleWebAuthorizationBroker.cs

Index: Src/GoogleApis.Auth.WP81/OAuth2/GoogleWebAuthorizationBroker.cs
===================================================================
new file mode 100644
--- /dev/null
 b/Src/GoogleApis.Auth.WP81/OAuth2/GoogleWebAuthorizationBroker.cs
@@ -0,0 1,107 @@
 /*
 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;
 }
 }
 }
 }