// Simple code snippet showing use of Google Service Account JSON key file within ServiceAccountCredential.

using System.IO;
using Google.Apis.Auth.OAuth2;
using Google.Apis.Calendar.v3;
using Google.Apis.Calendar.v3.Data;
using Google.Apis.Services;
using Newtonsoft.Json.Linq;

var serviceAccountJson = File.ReadAllText("<JSON-FILE-HERE>");

var o = JObject.Parse(serviceAccountJson);

var email = o["client_email"].ToString();
var privateKey = o["private_key"].ToString();

ServiceAccountCredential credential = new ServiceAccountCredential(
    new ServiceAccountCredential.Initializer(email)
    {
        Scopes = new[] { CalendarService.Scope.CalendarReadonly }
    }.FromPrivateKey(privateKey);
    
// Just an example initialising Calendar API
var service = new CalendarService(new BaseClientService.Initializer
{
    HttpClientInitializer = credential,
    ApplicationName = "APP-NAME-HERE"
});

// Then do what you like with the 'service' instance.