public class DemoSettings
{
 public string MainDomain { get; set; }
 public string SiteName { get; set; }
}

{
 "DemoSettings": {
 "MainDomain": "http://www.mysite.com",
 "SiteName": "My Main Site"
 },
 "Logging": {
 "IncludeScopes": false,
 "LogLevel": {
  "Default": "Debug",
  "System": "Information",
  "Microsoft": "Information"
 }
 }
}

public void ConfigureServices(IServiceCollection services)
{
 // Add framework services.
 services.AddMvc();
}

public void ConfigureServices(IServiceCollection services)
{
 // Add framework services.
 services.AddMvc();
 
 // Added - uses IOptions<T> for your settings.
 services.AddOptions();
 
 // Added - Confirms that we have a home for our DemoSettings
 services.Configure<DemoSettings>(Configuration.GetSection("DemoSettings"));
}

public class HomeController : Controller
{
 private DemoSettings ConfigSettings { get; set; }
 
 public HomeController(IOptions<DemoSettings> settings)
 {
  ConfigSettings = settings.Value;
 }
 
 public IActionResult Index()
 {
  ViewData["SiteName"] = ConfigSettings.SiteName;
  return View();
 }
}