using Microsoft.AspNetCore.Http;

public class HomeController:Controller
{
   public IActionResult Index()
   {
       HttpContext.Session.SetString("code","123456");
       return View(); 
    }

    public IActionResult About()
    {
       ViewBag.Code=HttpContext.Session.GetString("code");
       return View();
    }
}

public class SomeOtherClass
{
   private readonly IHttpContextAccessor _httpContextAccessor;
   private ISession _session=> _httpContextAccessor.HttpContext.Session;

   public SomeOtherClass(IHttpContextAccessor httpContextAccessor)
   {
      _httpContextAccessor=httpContextAccessor;       
   }

   public void Set()
   {
     _session.SetString("code","123456");
   }
  
   public void Get()
  {
     string code = _session.GetString("code");
   }
}

public static class SessionExtensions
{
   public static void SetObjectAsJson(this ISession session, string key, object value)
  {
    session.SetString(key, JsonConvert.SerializeObject(value));
  }

  public static T GetObjectFromJson<T>(this ISession session, string key)
  {
    var value = session.GetString(key);

    return value == null ? default(T) : JsonConvert.DeserializeObject<T>(value);
  }
}

var myComplexObject = new MyClass();
HttpContext.Session.SetObjectAsJson("Test", myComplexObject);


var myComplexObject = HttpContext.Session.GetObjectFromJson<MyClass>("Test");

// Microsoft SQL Server implementation of IDistributedCache.
// Note that this would require setting up the session state database.
services.AddSqlServerCache(o =>
{
  o.ConnectionString = "Server=.;Database=ASPNET5SessionState;Trusted_Connection=True;";
  o.SchemaName = "dbo";
  o.TableName = "Sessions";
});

// Redis implementation of IDistributedCache.
// This will override any previously registered IDistributedCache service.
services.AddSingleton<IDistributedCache, RedisCache>();