dotnet new mvc -o UserLoginApp
cd UserLoginApp 

using System.ComponentModel.DataAnnotations;

namespace UserLoginApp.Models
{
    public class User
    {
        [Required]
        public string Username { get; set; }

        [Required]
        public string Password { get; set; }
    }
} 

using System.ComponentModel.DataAnnotations;

namespace UserLoginApp.Models
{
    public class LoginViewModel
    {
        [Required]
        [Display(Name = "Kullanıcı Adı")]
        public string Username { get; set; }

        [Required]
        [DataType(DataType.Password)]
        [Display(Name = "Şifre")]
        public string Password { get; set; }
    }
} 

using Microsoft.AspNetCore.Mvc;
using UserLoginApp.Models;

namespace UserLoginApp.Controllers
{
    public class AccountController : Controller
    {
        [HttpGet]
        public IActionResult Login()
        {
            return View();
        }

        [HttpPost]
        public IActionResult Login(LoginViewModel model)
        {
            if (ModelState.IsValid)
            {
                // Bu kısımda kullanıcı doğrulama işlemleri yapılır
                if (model.Username == "admin" && model.Password == "password")
                {
                    return RedirectToAction("Index", "Home");
                }
                ModelState.AddModelError(string.Empty, "Geçersiz kullanıcı adı veya şifre.");
            }
            return View(model);
        }
    }
} 

@model UserLoginApp.Models.LoginViewModel

<h2>Kullanıcı Girişi</h2>

<form asp-action="Login" method="post">
    <div>
        <label asp-for="Username"></label>
        <input asp-for="Username" />
        <span asp-validation-for="Username" style="color:red"></span>
    </div>
    <div>
        <label asp-for="Password"></label>
        <input asp-for="Password" type="password" />
        <span asp-validation-for="Password" style="color:red"></span>
    </div>
    <div>
        <button type="submit">Giriş Yap</button>
    </div>
</form>

<div style="color:red">
    @Html.ValidationSummary()
</div> 

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery-validate/1.17.0/jquery.validate.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery-validation-unobtrusive/3.2.10/jquery.validate.unobtrusive.min.js"></script> 

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllersWithViews();
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseExceptionHandler("/Home/Error");
        app.UseHsts();
    }
    app.UseHttpsRedirection();
    app.UseStaticFiles();

    app.UseRouting();

    app.UseAuthentication();
    app.UseAuthorization();

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

dotnet run