Importing Gmail contacts to my website on a button click

 protected void btnInviteFriends_Click(object sender, EventArgs e)
        {
            const string clientID = "Your Client Id";
            const string clientSecret = "YourClientSecret";
// Page url to which           it should be redirected after accessing Contact API
            const string redirectUri = "https://YourDomain/Default.aspx";  

            AuthorizationServerDescription server = new AuthorizationServerDescription
            {
                AuthorizationEndpoint = new Uri("https://accounts.google.com/o/oauth2/auth"),
                TokenEndpoint = new Uri("https://accounts.google.com/o/oauth2/token"),
                ProtocolVersion = ProtocolVersion.V20,
            };
            List<string> scope = new List<string>
            {
                "https://mail.google.com/",
                "https://www.googleapis.com/auth/userinfo#email"
                 //GoogleScope.ImapAndSmtp.Name,
                 //GoogleScope.EmailAddressScope.Name 
            };

            //At this point user is redirected to Google to authorize the access:
            WebServerClient consumer = new WebServerClient(server, clientID, clientSecret);
            // Here redirect to authorization site occurs
            consumer.RequestUserAuthorization(scope, new Uri(redirectUri));

            //After this step user is redirected back to your website (ReDirect URL). Following is this callback code. Its purpose is to get a refresh-token and an access-token:

            consumer.ClientCredentialApplicator =
                ClientCredentialApplicator.PostParameter(clientSecret);
            IAuthorizationState grantedAccess = consumer.ProcessUserAuthorization(null);

            string accessToken = grantedAccess.AccessToken;


            GoogleApi api = new GoogleApi(accessToken);
            string user = api.GetEmail();

            using (Imap imap = new Imap())
            {
                imap.ConnectSSL("imap.gmail.com");
                imap.LoginOAUTH2(user, accessToken);

                imap.SelectInbox();
                List<long> uids = imap.Search(Flag.Unseen);

                foreach (long uid in uids)
                {
                    string eml = imap.GetMessageByUID(uid);
                    IMail email = new MailBuilder().CreateFromEml(eml);
                    Console.WriteLine(email.Subject);
                }
                imap.Close();
            }


            //Refreshing access token
            AuthorizationServerDescription authServer = new AuthorizationServerDescription
            {
                AuthorizationEndpoint =
                    new Uri("https://accounts.google.com/o/oauth2/auth?access_type=offline"),
            };

            grantedAccess = consumer.ProcessUserAuthorization(null);
            consumer.RefreshAuthorization(grantedAccess, TimeSpan.FromMinutes(20));


            authServer = new AuthorizationServerDescription
            {
                AuthorizationEndpoint =
                     new Uri("https://accounts.google.com/o/oauth2/auth?access_type=offline&approval_prompt=force"),
            };

        }