ASP.NET身份核心（ASP.NET Identity Core）是一个开源的、可扩展的身份验证和授权框架，用于构建基于ASP.NET Core的Web应用程序。

自托管身份验证（Self-hosted Authentication）指的是在应用程序中自己实现身份验证逻辑，而不是依赖于框架提供的身份验证机制。

第三方身份验证提供者（Third-party Authentication Providers）是指使用第三方服务提供商（如Google、Facebook、Twitter等）的身份验证服务来进行用户身份验证。

下面是一个示例，演示了如何使用ASP.NET身份核心、自托管身份验证和第三方身份验证提供者来实现身份验证：

ASP.NET身份核心示例：

// Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext(options =>
        options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

    services.AddDefaultIdentity(options => options.SignIn.RequireConfirmedAccount = true)
        .AddEntityFrameworkStores();

    services.AddControllersWithViews();
    services.AddRazorPages();
}

// HomeController.cs
public class HomeController : Controller
{
    private readonly UserManager _userManager;
    private readonly SignInManager _signInManager;

    public HomeController(UserManager userManager, SignInManager signInManager)
    {
        _userManager = userManager;
        _signInManager = signInManager;
    }

    public IActionResult Index()
    {
        return View();
    }

    [HttpPost]
    public async Task Login(LoginViewModel model)
    {
        if (ModelState.IsValid)
        {
            var result = await _signInManager.PasswordSignInAsync(model.Username, model.Password, false, lockoutOnFailure: false);
            if (result.Succeeded)
            {
                return RedirectToAction("Index", "Home");
            }
            else
            {
                ModelState.AddModelError(string.Empty, "Invalid login attempt.");
            }
        }
        return View(model);
    }

    // Other actions and views...
}

自托管身份验证示例：

// HomeController.cs
public class HomeController : Controller
{
    public IActionResult Index()
    {
        return View();
    }

    [HttpPost]
    public IActionResult Login(LoginViewModel model)
    {
        if (ModelState.IsValid)
        {
            // Your custom authentication logic here
            if (IsValidUser(model.Username, model.Password))
            {
                // Authentication successful
                return RedirectToAction("Index", "Home");
            }
            else
            {
                ModelState.AddModelError(string.Empty, "Invalid login attempt.");
            }
        }
        return View(model);
    }

    // Other actions and views...
}

第三方身份验证提供者示例：

// Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddAuthentication()
        .AddGoogle(options =>
        {
            options.ClientId = Configuration["Authentication:Google:ClientId"];
            options.ClientSecret = Configuration["Authentication:Google:ClientSecret"];
        })
        .AddFacebook(options =>
        {
            options.AppId = Configuration["Authentication:Facebook:AppId"];
            options.AppSecret = Configuration["Authentication:Facebook:AppSecret"];
        })
        .AddTwitter(options =>
        {
            options.ConsumerKey = Configuration["Authentication:Twitter:ConsumerKey"];
            options.ConsumerSecret = Configuration["Authentication:Twitter:ConsumerSecret"];
        });

    services.AddControllersWithViews();
    services.AddRazorPages();
}

// AccountController.cs
public class AccountController : Controller
{
    public IActionResult ExternalLogin(string provider)
    {
        var redirectUrl = Url.Action(nameof(ExternalLoginCallback), "Account");
        var properties = _signInManager.ConfigureExternalAuthenticationProperties(provider, redirectUrl);
        return Challenge(properties, provider);
    }

    public async Task ExternalLoginCallback()
    {
        var info = await _signInManager.GetExternalLoginInfoAsync();
        if (info == null)
        {
            // External authentication failed
            return RedirectToAction("Login");
        }

        // External authentication succeeded
        var result = await _signInManager.ExternalLoginSignInAsync(info.LoginProvider, info.ProviderKey, isPersistent: false, bypassTwoFactor: true);
        if (result.Succeeded)
        {
            return RedirectToAction("Index", "Home");
        }
        else
        {
            // New user, prompt for email
            var email = info.Principal.FindFirstValue(ClaimTypes.Email);
            return View("ExternalLoginConfirmation", new ExternalLoginConfirmationViewModel { Email = email });
        }
    }

    // Other actions and views...
}