Index.cshtml.cs

using AuthenticationSample.Models;
using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Authentication.Cookies;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.Extensions.Configuration;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Security.Claims;
using System.Threading.Tasks;

namespace AuthenticationSample.Pages
{
    public class IndexModel : PageModel
    {
        private readonly IConfiguration configuration;
        public IndexModel(IConfiguration configuration)
        {
            this.configuration = configuration;
        }

        [BindProperty]
        public string UserName { get; set; }
        [BindProperty, DataType(DataType.Password)]
        public string Password { get; set; }
        public string Message { get; set; }
        public async Task<IActionResult> OnPost()
        {
            var user = configuration.GetSection("SiteUser").Get<SiteUser>();
            
            if (UserName == user.UserName)
            {
                var passwordHasher = new PasswordHasher<string>();
                if (passwordHasher.VerifyHashedPassword(null, user.Password, Password) == PasswordVerificationResult.Success)
                {
                    var claims = new List<Claim>
                    {
                        new Claim(ClaimTypes.Name, UserName)
                    };
                    var claimsIdentity = new ClaimsIdentity(claims, CookieAuthenticationDefaults.AuthenticationScheme);
                    await HttpContext.SignInAsync(CookieAuthenticationDefaults.AuthenticationScheme, new ClaimsPrincipal(claimsIdentity));
                    return RedirectToPage("/admin/index");
                }
            }
            Message = "Invalid attempt";
            return Page();
        }
    }
}