What is a Session?
Session is KEY-VALUE structure to store the user specific data. In Asp.Net Core .NET 8 session is not enable by default, we have to enable it. Session data persists across multiple HTTP requests.

How many ways for Session storage?
In-Memory Cache: Server base storage. Storage capacity is depend upon server’s available memory. Best for single server base environment.
Distributed Cache: Session storage not on one server its store on multiple server. Distributed cache work with Redis, Sql Server etc. .

How to Enable Session in .Net 8 Asp.Net Core MVC Application?
builder.Services.AddSession();

Add another line just after app declaration line:
app.UseSession();

How to set or store the value in session?
Create or Setting Session value.

Syntax
HttpContext.Session.SetString(KEY,VALUE);
HttpContext.Session.SetInt22(KEY,VALUE);

Example
HttpContext.Session.SetString(“USERNAME”, UserName);
HttpContext.Session.SetString(“USERID”,Convert.ToString(UserID));

How to get or retrieve the value of session?
Getting Session value.

Syntax
HttpContext.Session.GetString(KEY);

HttpContext.Session.GetInt22(KEY);

Example
HttpContext.Session.GetString(“USERNAME”);

HttpContext.Session.GetString(“USERID”);

How to remove particular session key?
You can easily remove a specific session key.

Syntax
HttpContext.Session.Remove(KEY);

Example
HttpContext.Session.Remove(“UESERNAME”);

How to remove all session keys?
You can delete/remove/clear all sessions in one go.

HttpContext.Session.Clear();

Clear: It remove all the current session entries from the server.

OR

HttpContext.SignOutAsync();

SignOutAsync: It end the current user session and remove or clear the user’s authentication cookie from the server.
Walk-through on session implementation

In this article I had used Visual Studio 2022. After follow step by step you are able to implement SESSION in your Asp.Net Core project.

Above screenshot is a view of default project structure of Asp.Net Core .NET 8.

Now open program.cs file to add following line:
builder.Services.AddSession(); //

app.UseSession(); //after app declaration.

Update Program.cs file Code:
var builder = WebApplication.CreateBuilder(args);

// Add services to the container
builder.Services.AddControllersWithViews();

// Configure session service for the application
builder.Services.AddSession();

var app = builder.Build();

// Enable the Session Middleware
app.UseSession();

// Configure the HTTP request pipeline
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Home/Error");
    // The default HSTS value is 30 days. You may want to change this for production scenarios
    app.UseHsts();
}

app.UseHttpsRedirection();
app.UseStaticFiles();

app.UseRouting();

app.UseAuthorization();

app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}");

app.Run();

Open the HomeController.cs file from CONTROLLERS folder.

Update HomeController.cs file code:
using LearnCore.Models;
using Microsoft.AspNetCore.Mvc;
using System.Diagnostics;

namespace LearnCore.Controllers
{
    public class HomeController : Controller
    {
        private readonly ILogger<HomeController> _logger;

        public HomeController(ILogger<HomeController> logger)
        {
            _logger = logger;
        }

        public IActionResult Index()
        {
            // Create SESSION called USERNAME and store value "Peter Scott"
            HttpContext.Session.SetString("USERNAME", "Peter Scott");
            return View();
        }

        public IActionResult Privacy()
        {
            // Get value from SESSION
            string UserValName = HttpContext.Session.GetString("USERNAME")?.ToString();
            ViewBag.UserName = UserValName;
            return View();
        }

        [ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]
        public IActionResult Error()
        {
            return View(new ErrorViewModel { RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier });
        }
    }
}

Open the Privacy.cshtml file from VIEWS àHOME.

Update the Privacy.cshtml file code :
@{
    ViewData["Title"] = "Privacy Policy";
}

<h1>@ViewData["Title"]</h1>

<p>Use this page to detail your site's privacy policy.</p>

<h2>
    User Name: <i><u>@ViewBag.UserName</u></i>
</h2>

Now press F5 to run the project. Happy Coding!