How Google API V 3.0 .Net library and Google OAuth2 Handling refresh token

Question

In my application I am using Google API V 3.0 .Net library with Google OAuth2 to synchronize Google calender and outlook calender. I am using below code to get the Google.Apis.Calendar.v3.CalendarService service object. During authentication I stored the Json file and from that I am requesting for Google.Apis.Auth.OAuth2.UserCredential object.

private Google.Apis.Auth.OAuth2.UserCredential GetGoogleOAuthCredential()
{
    GoogleTokenModel _TokenData = new GoogleTokenModel();
    String JsonFilelocation = "jsonFileLocation;
    Google.Apis.Auth.OAuth2.UserCredential credential = null;
    using (var stream = new FileStream(JsonFilelocation, FileMode.Open,
                    FileAccess.Read))
    {
        Google.Apis.Auth.OAuth2.GoogleWebAuthorizationBroker.Folder = "Tasks.Auth.Store";
        credential = Google.Apis.Auth.OAuth2.GoogleWebAuthorizationBroker.AuthorizeAsync(
        Google.Apis.Auth.OAuth2.GoogleClientSecrets.Load(stream).Secrets,
        new[] { Google.Apis.Calendar.v3.CalendarService.Scope.Calendar },
        "user",
        CancellationToken.None,
        new FileDataStore("OGSync.Auth.Store")).Result;
    }
    return credential;
}

Requesting for Service object code is :

Google.Apis.Calendar.v3.CalendarService _V3calendarService = new Google.Apis.Calendar.v3.CalendarService(new Google.Apis.Services.BaseClientService.Initializer()
{
HttpClientInitializer = GetGoogleOAuthCredential(),
ApplicationName = "TestApplication",
});

Above code works fine to get the Calendarservice object. My question is, my Json file has refresh and access tokens. how the above code handles refresh token to obtain the service when access token expired? Because I need to call the Calendarservice object frequently, I like to implement singleton pattern for calenderService object. How to get Calendarservice without calling GetGoogleOAuthCredential frequently? Any help/guidance is appreciated.

Answer 1

Spent the last two days figuring this out myself. The library does not refresh the tokens automatically unless you specify "access_type=offline".

https://developers.google.com/api-client-library/dotnet/guide/aaa_oauth

I'm gonna paste the code I'm using and if there is anything you don't understand, just ask. I have read so many posts and I litteraly got this working right now so there is some commented code and it has not been refactored yet. I hope this will help someone. The NuGet packages I'm using are these:

Google.Apis.Auth.MVC

Google.Apis.Calendar.v3

Code:

AuthCallbackController:

[AuthorizationCodeActionFilter]
public class AuthCallbackController : Google.Apis.Auth.OAuth2.Mvc.Controllers.AuthCallbackController
{
protected static readonly ILogger Logger = ApplicationContext.Logger.ForType<AuthCallbackController>();

/// <summary>Gets the authorization code flow.</summary>
protected IAuthorizationCodeFlow Flow { get { return FlowData.Flow; } }

/// <summary>
/// Gets the user identifier. Potential logic is to use session variables to retrieve that information.
/// </summary>
protected string UserId { get { return FlowData.GetUserId(this); } }

/// <summary>
/// The authorization callback which receives an authorization code which contains an error or a code.
/// If a code is available the method exchange the coed with an access token and redirect back to the original
/// page which initialized the auth process (using the state parameter).
/// <para>
/// The current timeout is set to 10 seconds. You can change the default behavior by setting 
/// <see cref="System.Web.Mvc.AsyncTimeoutAttribute"/> with a different value on your controller.
/// </para>
/// </summary>
/// <param name="authorizationCode">Authorization code response which contains the code or an error.</param>
/// <param name="taskCancellationToken">Cancellation token to cancel operation.</param>
/// <returns>
/// Redirect action to the state parameter or <see cref="OnTokenError"/> in case of an error.
/// </returns>
[AsyncTimeout(60000)]
public async override Task<ActionResult> IndexAsync(AuthorizationCodeResponseUrl authorizationCode,
   CancellationToken taskCancellationToken)
{
    if (string.IsNullOrEmpty(authorizationCode.Code))
    {
        var errorResponse = new TokenErrorResponse(authorizationCode);
        Logger.Info("Received an error. The response is: {0}", errorResponse);
        Debug.WriteLine("Received an error. The response is: {0}", errorResponse);
        return OnTokenError(errorResponse);
    }

    Logger.Debug("Received \"{0}\" code", authorizationCode.Code);
    Debug.WriteLine("Received \"{0}\" code", authorizationCode.Code);


    var returnUrl = Request.Url.ToString();
    returnUrl = returnUrl.Substring(0, returnUrl.IndexOf("?"));

    var token = await Flow.ExchangeCodeForTokenAsync(UserId, authorizationCode.Code, returnUrl,
        taskCancellationToken).ConfigureAwait(false);

    // Extract the right state.
    var oauthState = await AuthWebUtility.ExtracRedirectFromState(Flow.DataStore, UserId,
        authorizationCode.State).ConfigureAwait(false);

    return new RedirectResult(oauthState);
}

protected override Google.Apis.Auth.OAuth2.Mvc.FlowMetadata FlowData
{
    get { return new AppFlowMetadata(); }
}

protected override ActionResult OnTokenError(TokenErrorResponse errorResponse)
{
    throw new TokenResponseException(errorResponse);
}


//public class AuthCallbackController : Google.Apis.Auth.OAuth2.Mvc.Controllers.AuthCallbackController
//{
//    protected override Google.Apis.Auth.OAuth2.Mvc.FlowMetadata FlowData
//    {
//        get { return new AppFlowMetadata(); }
//    }
//}

}

Method for Controller calling Google API

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

        if (result.Credential != null)
        {
            //var ttt = await result.Credential.RevokeTokenAsync(cancellationToken);

            //bool x = await result.Credential.RefreshTokenAsync(cancellationToken);

            var service = new CalendarService(new BaseClientService.Initializer()
            {
                HttpClientInitializer = result.Credential,
                ApplicationName = "GoogleApplication",
            });
            var t = service.Calendars;

            var tt = service.CalendarList.List();

            // Define parameters of request.
            EventsResource.ListRequest request = service.Events.List("primary");
            request.TimeMin = DateTime.Now;
            request.ShowDeleted = false;
            request.SingleEvents = true;
            request.MaxResults = 10;
            request.OrderBy = EventsResource.ListRequest.OrderByEnum.StartTime;

            // List events.
            Events events = request.Execute();
            Debug.WriteLine("Upcoming events:");
            if (events.Items != null && events.Items.Count > 0)
            {
                foreach (var eventItem in events.Items)
                {
                    string when = eventItem.Start.DateTime.ToString();
                    if (String.IsNullOrEmpty(when))
                    {
                        when = eventItem.Start.Date;
                    }
                    Debug.WriteLine("{0} ({1})", eventItem.Summary, when);
                }
            }
            else
            {
                Debug.WriteLine("No upcoming events found.");
            }


            //Event myEvent = new Event
            //{
            //    Summary = "Appointment",
            //    Location = "Somewhere",
            //    Start = new EventDateTime()
            //        {
            //            DateTime = new DateTime(2014, 6, 2, 10, 0, 0),
            //            TimeZone = "America/Los_Angeles"
            //        },
            //    End = new EventDateTime()
            //        {
            //            DateTime = new DateTime(2014, 6, 2, 10, 30, 0),
            //            TimeZone = "America/Los_Angeles"
            //        },
            //    Recurrence = new String[] {
            //        "RRULE:FREQ=WEEKLY;BYDAY=MO"
            //        },
            //    Attendees = new List<EventAttendee>()
            //        {
            //        new EventAttendee() { Email = "[email protected]" }
            //        }
            //};

            //Event recurringEvent = service.Events.Insert(myEvent, "primary").Execute();

            return View();
        }
        else
        {
            return new RedirectResult(result.RedirectUri);
        }
    }

Derived class of FlowMetadata

public class AppFlowMetadata : FlowMetadata
    {
        //static readonly string server = ConfigurationManager.AppSettings["DatabaseServer"];
        //static readonly string serverUser = ConfigurationManager.AppSettings["DatabaseUser"];
        //static readonly string serverPassword = ConfigurationManager.AppSettings["DatabaseUserPassword"];
        //static readonly string serverDatabase = ConfigurationManager.AppSettings["DatabaseName"];
    ////new FileDataStore("Daimto.GoogleCalendar.Auth.Store")
    ////new FileDataStore("Drive.Api.Auth.Store")
    //static DatabaseDataStore databaseDataStore = new DatabaseDataStore(server, serverUser, serverPassword, serverDatabase);


    private static readonly IAuthorizationCodeFlow flow =
new ForceOfflineGoogleAuthorizationCodeFlow(new GoogleAuthorizationCodeFlow.Initializer
{
    ClientSecrets = new ClientSecrets
    {
        ClientId = "yourClientId",
        ClientSecret = "yourClientSecret"

    },
    Scopes = new[]
    {
CalendarService.Scope.Calendar, // Manage your calendars
//CalendarService.Scope.CalendarReadonly // View your Calendars
    },
    DataStore = new EFDataStore(),
});

    public override string GetUserId(Controller controller)
    {
        // In this sample we use the session to store the user identifiers.
        // That's not the best practice, because you should have a logic to identify
        // a user. You might want to use "OpenID Connect".
        // You can read more about the protocol in the following link:
        // https://developers.google.com/accounts/docs/OAuth2Login.

        //var user = controller.Session["user"];
        //if (user == null)
        //{
        //    user = Guid.NewGuid();
        //    controller.Session["user"] = user;
        //}
        //return user.ToString();

        //var store = new UserStore<ApplicationUser>(new ApplicationDbContext());
        //var manager = new UserManager<ApplicationUser>(store);
        //var currentUser = manager.FindById(controller.User.Identity.GetUserId());

        return controller.User.Identity.GetUserId();

    }

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

    public override string AuthCallback
    {
        get { return @"/GoogleApplication/AuthCallback/IndexAsync"; }
    }
}

Entity framework 6 DataStore class

 public class EFDataStore : IDataStore
    {
        public async Task ClearAsync()
        {
            using (var context = new ApplicationDbContext())
            {
                var objectContext = ((IObjectContextAdapter)context).ObjectContext;
                await objectContext.ExecuteStoreCommandAsync("TRUNCATE TABLE [Items]");
            }
        }

        public async Task DeleteAsync<T>(string key)
        {
            if (string.IsNullOrEmpty(key))
            {
                throw new ArgumentException("Key MUST have a value");
            }

        using (var context = new ApplicationDbContext())
        {
            var generatedKey = GenerateStoredKey(key, typeof(T));
            var item = context.GoogleAuthItems.FirstOrDefault(x => x.Key == generatedKey);
            if (item != null)
            {
                context.GoogleAuthItems.Remove(item);
                await context.SaveChangesAsync();
            }
        }
    }

    public Task<T> GetAsync<T>(string key)
    {
        if (string.IsNullOrEmpty(key))
        {
            throw new ArgumentException("Key MUST have a value");
        }

        using (var context = new ApplicationDbContext())
        {
            var generatedKey = GenerateStoredKey(key, typeof(T));
            var item = context.GoogleAuthItems.FirstOrDefault(x => x.Key == generatedKey);
            T value = item == null ? default(T) : JsonConvert.DeserializeObject<T>(item.Value);
            return Task.FromResult<T>(value);
        }
    }

    public async Task StoreAsync<T>(string key, T value)
    {
        if (string.IsNullOrEmpty(key))
        {
            throw new ArgumentException("Key MUST have a value");
        }

        using (var context = new ApplicationDbContext())
        {
            var generatedKey = GenerateStoredKey(key, typeof(T));
            string json = JsonConvert.SerializeObject(value);

            var item = await context.GoogleAuthItems.SingleOrDefaultAsync(x => x.Key == generatedKey);

            if (item == null)
            {
                context.GoogleAuthItems.Add(new GoogleAuthItem { Key = generatedKey, Value = json });
            }
            else
            {
                item.Value = json;
            }

            await context.SaveChangesAsync();
        }
    }

    private static string GenerateStoredKey(string key, Type t)
    {
        return string.Format("{0}-{1}", t.FullName, key);
    }
}

Derived class for GoogleAuthorizationCodeFlow. Enabling long-lived refresh token that take care of automatically "refreshing" the token, which simply means getting a new access token.

https://developers.google.com/api-client-library/dotnet/guide/aaa_oauth

internal 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"
        };
    }
}

GoogleAuthItem is used with EFDataStore

public class GoogleAuthItem
{
    [Key]
    [MaxLength(100)]
    public string Key { get; set; }

    [MaxLength(500)]
    public string Value { get; set; }
}

public DbSet<GoogleAuthItem> GoogleAuthItems { get; set; }

Answer 2

That's the butty of the client library! this magic is done for you automatically :)

UserCredential implements both IHttpExecuteInterceptor and IHttpUnsuccessfulResponseHandler. so whenever the access token is going to be expired, or is already expired, the client makes a call to the authorization server to refresh the token and get a new access token (which is valid for the next 60 minutes).

Read more about it at https://developers.google.com/api-client-library/dotnet/guide/aaa_oauth#credentials