Issue 463: Provide a signout\logout method

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

 /*
 Copyright 2013 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
@@ skipping 57 matching lines @@
 IEnumerable<string> scopes, string user, CancellationToken taskCance
llationToken)
 {
 var initializer = new GoogleAuthorizationCodeFlow.Initializer
 {
 ClientSecretsStream = clientSecretsStream,
 };
 
 return await AuthorizeAsyncCore(initializer, scopes, user, taskCance
llationToken).ConfigureAwait(false);
 }
 
+/// <summary>
+/// Asynchronously reauthorizes the user. This method should be called i
f the users want to authorize after·
+/// they revoked the token.
+/// </summary>
+/// <param name="userCredential">The current user credential. Its <see c
ref="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(userCredentia
l.Flow);
+// Create an authorization code installed app instance and authorize
the user.
+UserCredential newUserCredential = await installedApp.AuthorizeAsync
(userCredential.UderId,
+taskCancellationToken).ConfigureAwait(false);
+userCredential.Token = newUserCredential.Token;
+}
+
 /// <summary>The core logic for asynchronously authorizing the specified
user.</summary>
 /// <param name="initializer">The authorization code initializer.</param
>
 /// <param name="scopes">
 /// The scopes which indicate the Google API access your application is
requesting.
 /// </param>
 /// <param name="user">The user to authenticate.</param>
 /// <param name="taskCancellationToken">Cancellation token to cancel an
operation.</param>
 /// <returns>User credential.</returns>
- private static async Task<UserCredential> AuthorizeAsyncCore(Authorizati
 onCodeFlow.Initializer initializer,
- IEnumerable<string> scopes, string user, CancellationToken taskCance
 llationToken)
+ private static async Task<UserCredential> AuthorizeAsyncCore(
+ GoogleAuthorizationCodeFlow.Initializer initializer, IEnumerable<str
 ing> scopes, string user,
+ CancellationToken taskCancellationToken)
 {
 initializer.Scopes = scopes;
 initializer.DataStore = new StorageDataStore();
 
- var installedApp = new AuthorizationCodeWPInstalledApp(initializer);
+ var installedApp = new AuthorizationCodeWPInstalledApp(new GoogleAut
 horizationCodeFlow(initializer));
 return await installedApp.AuthorizeAsync(user, taskCancellationToken
).ConfigureAwait(false);
 }
 }
 }