使用GoogleAuthorizationCodeFlow进行身份验证时保持RefreshToken

Question

       var REFRESH_TOKEN = System.Configuration.ConfigurationSettings.AppSettings["AdxToken"].ToString();
        ClientSecrets secrets = new ClientSecrets()
        {
            ClientId = clienID,
            ClientSecret = clientSecret
        };

        var token = new TokenResponse { RefreshToken = REFRESH_TOKEN };

        var credentials = new UserCredential(new GoogleAuthorizationCodeFlow(
                         new GoogleAuthorizationCodeFlow.Initializer
                      {
                          ClientSecrets = secrets
                      }),
                      "user",
                      token);

我使用上面的方法来验证客户端。我希望自动化我的流程每天运行，问题是上面代码中使用的RefreshToken每两天过期一次。 以下是获取RefreshToken

的代码

     private OAuth2Authenticator<WebServerClient> CreateAuthenticator()
    {
        // Register the authenticator.
        var provider = new WebServerClient(GoogleAuthenticationServer.Description);
        provider.ClientIdentifier = ClientCredentials.ClientID;
        provider.ClientSecret = ClientCredentials.ClientSecret;
        var authenticator = new OAuth2Authenticator<WebServerClient>(provider, GetAuthentication);
        //{ NoCaching = true }; // TODO(mlinder): Uncomment when CL is merged.
        return authenticator;
    }

      private IAuthorizationState GetAuthentication(WebServerClient client)
    {
        // If this user is already authenticated, then just return the auth state.
        IAuthorizationState state = AuthState;
        if (state != null)
        {
            return state;
        }

        // Check if an authorization request already is in progress.
        state = client.ProcessUserAuthorization(new HttpRequestInfo(HttpContext.Current.Request));
        if (state != null && (!string.IsNullOrEmpty(state.AccessToken) || !string.IsNullOrEmpty(state.RefreshToken)))
        {
            // Store and return the credentials.
            HttpContext.Current.Session["AUTH_STATE"] = _state = state;
            return state;
        }

        OutgoingWebResponse response = client.PrepareRequestUserAuthorization(new[] { "https://www.googleapis.com/auth/adexchange.seller", "https://www.googleapis.com/auth/adexchange.seller.readonly" });

       response.Headers["Location"] += "&access_type=offline&approval_prompt=force";
        response.Send(); // Will throw a ThreadAbortException to prevent sending another response.
        return null;


    }

有没有办法坚持这个RefreshToken，因为我的任务不能在没有这个的情况下实现自动化？