DiunaBI/WebAPI/GoogleSheetsHelper.cs

using Google.Apis.Auth.OAuth2;
using Google.Apis.Services;
using Google.Apis.Sheets.v4;

namespace WebAPI
{
    public class GoogleSheetsHelper
    {
        public SheetsService Service { get; set; }
        const string APPLICATION_NAME = "Diuna";
        static readonly string[] Scopes = { SheetsService.Scope.Spreadsheets };
        public GoogleSheetsHelper()
        {
            InitializeService();
        }
        private void InitializeService()
        {
            var credential = GetCredentialsFromFile();
            Service = new SheetsService(new BaseClientService.Initializer()
            {
                HttpClientInitializer = credential,
                ApplicationName = APPLICATION_NAME
            });
        }
        private GoogleCredential GetCredentialsFromFile()
        {
            string fileName = "client_secrets.json";
#if DEBUG
            fileName = "client_secrets.Development.json";
#endif
            GoogleCredential credential;
            using (var stream = new FileStream(fileName, FileMode.Open, FileAccess.Read))
            {
                credential = GoogleCredential.FromStream(stream).CreateScoped(Scopes);
            }
            return credential;
        }
    }
}