Issue 351: Reimplement OAuth2 (Step 3 - Tests, Flows and Credential)

Src/GoogleApis.Auth/OAuth2/AuthorizationCodeInstalledApp.cs

Index: Src/GoogleApis.Auth/OAuth2/AuthorizationCodeInstalledApp.cs
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 b/Src/GoogleApis.Auth/OAuth2/AuthorizationCodeInstalledApp.cs
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 /*
 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
 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.Threading;
 using System.Threading.Tasks;
 using Google.Apis.Auth.OAuth2.Responses;
 using Google.Apis.Auth.OAuth2.Requests;
 using Google.Apis.Logging;
 namespace Google.Apis.Auth.OAuth2
 {
 /// <summary>
 /// Thread-safe OAuth 2.0 authorization code flow for an installed application that persists end-user credentials.
 /// </summary>
 public class AuthorizationCodeInstalledApp : IAuthorizationCodeInstalledApp
 {
 private static readonly ILogger Logger = ApplicationContext.Logger.ForType<AuthorizationCodeInstalledApp>();
 private readonly IAuthorizationCodeFlow flow;
 private readonly ICodeReceiver codeReceiver;
 /// <summary>
 /// Constructs a new authorization code installed application with the given flow and code receiver.
 /// </summary>
 public AuthorizationCodeInstalledApp(IAuthorizationCodeFlow flow, ICodeReceiver codeReceiver)
 {
 this.flow = flow;
 this.codeReceiver = codeReceiver;
 }
 #region IAuthorizationCodeInstalledApp Members
 /// <summary>Gets the authorization code flow.</summary>
 public IAuthorizationCodeFlow Flow
 {
 get { return flow; }
 }
 /// <summary>Gets the code receiver which is responsible for receiving the authorization code.</summary>
 public ICodeReceiver CodeReceiver
 {
 get { return codeReceiver; }
 }
 public async Task<UserCredential> Authorize(string userId, CancellationToken taskCancellationToken)
 {
 // Try to load a token from the data store.
 var token = await Flow.LoadTokenAsync(userId, taskCancellationToken).ConfigureAwait(false);
 // If the stored token is null or it doesn't have a refresh token and the access token is expired we need
 // to retrieve a new authorization code.
 if (token == null || (token.RefreshToken == null && token.IsExpired(flow.Clock)))
 {
 // Create a authorization code request.
 var redirectUri = CodeReceiver.RedirectUri;
 AuthorizationCodeRequestUrl codeRequest = Flow.CreateAuthorizationCodeRequest(redirectUri);
 // Receive the code.
 var response = await CodeReceiver.ReceiveCodeAsync(codeRequest, taskCancellationToken)
 .ConfigureAwait(false);
 if (string.IsNullOrEmpty(response.Code))
 {
 var errorResponse = new TokenErrorResponse(response);
 Logger.Info("Received an error. The response is: {0}", errorResponse);
 throw new TokenResponseException(errorResponse);
 }
 Logger.Debug("Received \"{0}\" code", response.Code);
 // Get the token based on the code.
 token = await Flow.ExchangeCodeForTokenAsync(userId, response.Code, CodeReceiver.RedirectUri,
 taskCancellationToken).ConfigureAwait(false);
 }
 return new UserCredential(flow, userId, token);
 }
 #endregion
 }
 }