asp.net-mvc – OAuth 2 Google API刷新令牌为空

我正在开发一个Asp.NET MVC5 App following this Google sample code.

我希望应用程序经过身份验证并由用户创建一个accessstoken(配置阶段),之后我需要能够使用刷新令牌调用Google APis(在我的情况下为Directory API)(无需用户干预,如“离线”).

控制器：

public async Task<ActionResult> IndexAsync(CancellationToken cancellationToken)
{
    var result = await new AuthorizationCodeMvcApp(this, new AppFlowMetadata()).
                        AuthorizeAsync(cancellationToken);

        if (result.Credential != null)
        {
          var service = new Google.Apis.Admin.Directory.directory_v1.DirectoryService(new BaseClientService.Initializer
                        {
                            HttpClientInitializer = result.Credential,
                            ApplicationName = "My Application"
                        });
                      return View();
        }
        else
        {
             return new RedirectResult(result.RedirectUri);
        }
}

FlowMetadata实现. (我使用FiledataStore稍加修改(GoogleFileDataStore))

public class AppFlowMetadata : FlowMetadata
    {
        //Move to settings
        static readonly string clientId = "xxxccnvofsdfsfoj.apps.googleusercontent.com";
        static readonly string clientsecret = "xxxxxxxxxxLvtC6Qbqpp4x_";
        static readonly string datastore = "AdminSDK.Api.Auth.Store";


         private static readonly IAuthorizationCodeFlow flow =
            new GoogleAuthorizationCodeFlow(new GoogleAuthorizationCodeFlow.Initializer
                {
                    ClientSecrets = new ClientSecrets
                    {
                        ClientId = clientId,
                        ClientSecret = clientsecret
                    },
                    Scopes = new[] { DirectoryService.Scope.AdminDirectoryUser, DirectoryService.Scope.AdminDirectoryUserAliasReadonly },
                    DataStore = new GoogleFileDataStore(datastore)
                });


        public override string GetUserId(Controller controller)
        {           
            return ConfigHelper.UserID.ToString();
        }

        public override IAuthorizationCodeFlow Flow
        {
            get { return flow; }
        }
    }

当我调用IndexAsync控制器时,由于用户没有先前的accessstoken,它会在用户登录Google帐户后创建一个新的.
这是一个示例访问,

{“access_token”：“ya29.5gBOszGO-oYJJt4YZfF6FeaZth1f69 _…..”,“token_type”：“Bearer”,“expires_in”：3600,“Issued”：“2014-12-24T16：02：32.014 05:30” }

问题1：为什么没有存储Refreshtoken？如何检索refreshtoken？
问题2：如果我获得了refreshtoken,我应该如何修改代码以创建新的访问令牌并调用API(当accesstoken过期时)？
[我提到了this question,但缺少刷新令牌没有正确答案.

找到了Google API离线访问的解决方案,以获取刷新令牌并使用刷新令牌创建新的accessstoken,

问题1：为什么没有存储Refreshtoken？如何检索refreshtoken？

我必须在请求中将access_type设置为脱机(默认情况下是在线). as mentioned here

我必须为GoogleAuthorizationCodeFlow类编写自己的实现.感谢this post.

public class ForceOfflineGoogleAuthorizationCodeFlow : GoogleAuthorizationCodeFlow
    {
        public ForceOfflineGoogleAuthorizationCodeFlow(GoogleAuthorizationCodeFlow.Initializer initializer) : base(initializer) { }

        public override AuthorizationCodeRequestUrl CreateAuthorizationCodeRequest(string redirectUri)
        {
            return new GoogleAuthorizationCodeRequestUrl(new Uri(AuthorizationServerUrl))
            {
                ClientId = ClientSecrets.ClientId,
                Scope = string.Join(" ", Scopes),
                RedirectUri = redirectUri,
                AccessType = "offline",
                ApprovalPrompt = "force"
            };
        }
    };

问题2：..我应该修改代码来创建新的访问令牌并调用API吗？

//try to get results
    var result = await new AuthorizationCodeMvcApp(this, new AppFlowMetadata()).
                    AuthorizeAsync(cancellationToken);


    //// This bit checks if the token is out of date, 
    //// and refreshes the access token using the refresh token.
    if (result.Credential.Token.IsExpired(SystemClock.Default))
    {
           Google.Apis.Auth.OAuth2.Responses.TokenResponse token = new Google.Apis.Auth.OAuth2.Responses.TokenResponse();
           //If the token is expired recreate the token
           token = await result.Credential.Flow.RefreshTokenAsync(ConfigHelper.UserID.ToString(), result.Credential.Token.RefreshToken, CancellationToken.None);

            //Get the authorization details back
            result = await new AuthorizationCodeMvcApp(this, new AppFlowMetadata()).AuthorizeAsync(cancellationToken);
     }

这对我有用！希望这会有助于其他人……