在ASP.Net Core中，可以使用基于弹出式认证来实现用户认证。下面是一个基本示例：

1.在Startup.cs文件的ConfigureServices方法中添加以下代码：

services.AddAuthentication(options => { options.DefaultScheme = "CookieAuthentication"; options.DefaultChallengeScheme = "CustomScheme"; }) .AddCookie("CookieAuthentication", options => { options.LoginPath = "/Users/Login"; }) .AddOAuth("CustomScheme", options => { options.ClientId = ""; options.ClientSecret = ""; options.CallbackPath = new PathString("/oauth/callback"); options.AuthorizationEndpoint = ""; options.TokenEndpoint = ""; options.Scope.Add(""); options.SaveTokens = true;

    options.ClaimActions.MapJsonKey(ClaimTypes.NameIdentifier, "id");
    options.ClaimActions.MapJsonKey(ClaimTypes.Name, "username");
    options.ClaimActions.MapJsonKey(ClaimTypes.Email, "email");
});

2.在Startup.cs文件的Configure方法中添加以下代码：

app.UseAuthentication();

3.在控制器中添加以下代码，以在用户单击“登录”按钮时触发基于弹出式认证的流程：

[AllowAnonymous] public IActionResult Login(string returnUrl = "/") { var redirectUrl = Url.Action("Callback", "OAuth", new { ReturnUrl = returnUrl }); var properties = signInManager.ConfigureExternalAuthenticationProperties("CustomScheme", redirectUrl);

return Challenge(properties, "CustomScheme");

}

4.在控制器中添加以下代码，以在用户输入凭据并授权后处理回调：

public async Task Callback(string returnUrl = "/") { var result = await signInManager.ExternalLoginSignInAsync("CustomScheme", "", false);

if (result.Succeeded)
{
    return Redirect(returnUrl);
}

var info = await signInManager.GetExternalLoginInfoAsync();

if (info == null)
{
    return RedirectToAction("Login");
}

var user = new ApplicationUser
{
    UserName = info.Principal.FindFirstValue(ClaimTypes.Name),
    Email = info