[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> Login(LoginModel model)
{
    if (ModelState.IsValid)
    {
        User user = await db.Users.FirstOrDefaultAsync(u => u.Email == model.Email && u.Password == model.Password);
        if (user != null)
        {
            await Authenticate(model.Email); // аутентификация
 
            return RedirectToAction("Index", "Home");
        }
        ModelState.AddModelError("", "Некорректные логин и(или) пароль");
    }
    return View(model);
}

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Authorization;
 
public class HomeController : Controller
{
    [Authorize]
    public IActionResult Index()
    {
        return Content(User.Identity.Name);
    }
    // остальные методы
}