Issue 463: Provide a signout\logout method

Src/GoogleApis.Auth/OAuth2/Flows/IAuthorizationCodeFlow.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 50 matching lines @@
 CancellationToken taskCancellationToken);
 
 /// <summary>Asynchronously refreshes an access token using a refresh to
ken.</summary>
 /// <param name="userId">User identifier.</param>
 /// <param name="refreshToken">Refresh token which is used to get a new
access token.</param>
 /// <param name="taskCancellationToken">Cancellation token to cancel ope
ration.</param>
 /// <returns>Token response which contains the access token and the inpu
t refresh token.</returns>
 Task<TokenResponse> RefreshTokenAsync(string userId, string refreshToken
,
 CancellationToken taskCancellationToken);
 
- /// <summary>Asynchronously revokes the specified token.</summary>
+ /// <summary>
+ /// Asynchronously revokes the specified token. This method disconnects 
 the user's account from the OAuth 2.0
+ /// application. It should be called upon removing the user account from
  the site.</summary>
 /// <remarks>
- /// If revoking the token have been succeeded, the user's credential is 
 removed from the data store.

[class, 2014/05/12 18:00:53]

If revoking the token succeeds, the user's credential is removed from the data
store and the user must authorize again before your application can access that
user's resources made available to your application.

[peleyal, 2014/05/12 20:26:34]

Let me know, it is OK
On 2014/05/12 18:00:53, class wrote:

+ /// If revoking the token succeeds, the user's credential is removed fro
 m the data store and the user MUST
+ /// authorize the application again before the application can access th
 e user's private resources.
 /// </remarks>
 /// <param name="userId">User identifier.</param>
 /// <param name="token">Access token to be revoked.</param>
 /// <param name="taskCancellationToken">Cancellation token to cancel ope
ration.</param>
 /// <returns><c>true</c> if the token was revoked successfully.</returns
>········
 Task RevokeTokenAsync(string userId, string token, CancellationToken tas
kCancellationToken);
 }
 }