have a look into below URL

https://docs.microsoft.com/en-us/aspnet/core/fundamentals/app-state?view=aspnetcore-3.1

1)First, add dependency in project.json - "Microsoft.AspNetCore.Session",2)In startup.cs and add AddSession() and AddDistributedMemoryCache() lines to the ConfigureServices like this-services.AddDistributedMemoryCache(); //This way ASP.NET Core will use a Memory Cache to store session variables services.AddSession(options =>{options.IdleTimeout = TimeSpan.FromDays(1); // It depends on user requirements.options.CookieName = ".My.Session"; // Give a cookie name for session which will be visible in request payloads.}); 3)Add the UseSession() call in Configure method of startup like this-app.UseSession(); //make sure add this line before UseMvc() 4)In Controller, Session object can be used like this-using Microsoft.AspNetCore.Http;public class HomeController : Controller {public IActionResult Index(){ HttpContext.Session.SetString("SessionVariable1", "Testing123");return View();}public IActionResult About(){ViewBag.Message = HttpContext.Session.GetString("SessionVariable1");return View();} } If you are using cors policy then sometimes it may give errors, after enabling session regarding headers about enabling AllowCredentials header and using WithOrigins header instead of AllowAllOrigins.

The Microsoft.AspNetCore.Session package:

• Is included implicitly by the framework.
• Provides middleware for managing session state.

To enable the session middleware, Startup must contain:

1. Any of the IDistributedCache memory caches. The IDistributedCache implementation is used as a backing store for session. For more information, see Distributed caching in ASP.NET Core.
2. A call to AddSession in ConfigureServices.
3. A call to UseSession in Configure.

public void ConfigureServices(IServiceCollection services)
{
        services.AddDistributedMemoryCache();
        services.AddSession(options =>
 {
            options.IdleTimeout = TimeSpan.FromSeconds(10);
            options.Cookie.HttpOnly = true;
            options.Cookie.IsEssential = true;
 });
 //services.AddControllersWithViews();
 //services.AddRazorPages();
}

app.UseSession(); in Configure method of startup.cs class.

this way you can enable session in asp.net core