How to access users calendar list and events from google api using access token and refresh token

I have found solution using Google.Apis.Calendar.v3, i am posting it here so may help someone else. Following is the code to get the events list when you have refresh token of a user:

First get new access token using the refresh token:

string postString = "client_id=yourclientid";postString += "&client_secret=youclientsecret&refresh_token=userrefreshtoken";postString += "&grant_type=refresh_token";string url = "https://www.googleapis.com/oauth2/v4/token";HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url.ToString());request.Method = "POST";request.ContentType = "application/x-www-form-urlencoded";UTF8Encoding utfenc = new UTF8Encoding();byte[] bytes = utfenc.GetBytes(postString);Stream os = null;    request.ContentLength = bytes.Length;    os = request.GetRequestStream();    os.Write(bytes, 0, bytes.Length);    GoogleToken token = new GoogleToken();    HttpWebResponse webResponse = (HttpWebResponse)request.GetResponse();    Stream responseStream = webResponse.GetResponseStream();    StreamReader responseStreamReader = new StreamReader(responseStream);    string result = responseStreamReader.ReadToEnd();    JavaScriptSerializer serializer = new JavaScriptSerializer();    token = serializer.Deserialize<GoogleToken>(result);

Then use the toke and refresh token to create credentials.

var flow = new GoogleAuthorizationCodeFlow(new GoogleAuthorizationCodeFlow.Initializer            {                ClientSecrets = new ClientSecrets                {                    ClientId = yourclientid,                    ClientSecret = yourclientsecret                },                Scopes = new[] { CalendarService.Scope.Calendar }            });            var credential = new UserCredential(flow, Environment.UserName, new TokenResponse            {                AccessToken = token.access_token,                RefreshToken = userrefreshtoke            });            CalendarService service = new CalendarService(new BaseClientService.Initializer()            {                HttpClientInitializer = credential,                ApplicationName = "application name",            });            var list = service.CalendarList.List().Execute().Items;            foreach (var c in list)            {                var events = service.Events.List(c.Id).Execute().Items.Where(i => i.Start.DateTime >= DateTime.Now).ToList();                foreach (var e in events)                {                }}

GoogleToken class:

 public class GoogleToken    {        public string access_token { get; set; }        public string token_type { get; set; }        public string expires_in { get; set; }           }

According to the .NET Quickstart sample provided by Google you'll be needing to download a client_secret.json which is part of the authentication process. Check the whole process in the link.

Here' a snippet for feching events in .NET:

// List events.Events events = request.Execute();Console.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;}Console.WriteLine("{0} ({1})", eventItem.Summary, when);}}else{Console.WriteLine("No upcoming events found.");}Console.Read();

You can also read more of oAuth related guides in .NET here.

For more info on retrieving Calendar lists and events, read this guide.