如何在MVC中使用Facebook c# SDK获得生日(和其他字段)的权限

我正在构建一个MVC 4网站，允许用户通过Facebook登录。所有这些都像开箱即用的魅力。

但是现在我无法从Facebook获取用户的生日。我已经从Nuget安装了最新版本的Facebook c# SDK(6.1.4)。我已经在Facebook上设置了我的应用程序来请求user_birthday的权限。当我看到登录对话框预览生日是在权限列表。

当我运行我的MVC应用程序并通过我自己的facebook帐户登录时，我得到我的生日在响应中，但只要我使用不同的帐户登录，没有生日传递回来，也没有登录对话框，用户可以授予我的应用程序使用生日字段的权限。下面是我的ExternalLoginCallback()操作的完整代码:

[AllowAnonymous]
public ActionResult ExternalLoginCallback(string returnUrl)
{
    AuthenticationResult result = OAuthWebSecurity.VerifyAuthentication(Url.Action("ExternalLoginCallback", new { ReturnUrl = returnUrl }));
    if (!result.IsSuccessful)
    {
        return RedirectToAction("ExternalLoginFailure");
    }
    // Get the Facebook access token
    if (result.ExtraData.Keys.Contains("accesstoken"))
    {
        Session["facebooktoken"] = result.ExtraData["accesstoken"];
    }
    if (OAuthWebSecurity.Login(result.Provider, result.ProviderUserId, createPersistentCookie: false))
    {
        return RedirectToLocal(returnUrl);
    }
    if (User.Identity.IsAuthenticated)
    {
        // If the current user is logged in add the new account
        OAuthWebSecurity.CreateOrUpdateAccount(result.Provider, result.ProviderUserId, User.Identity.Name);
        return RedirectToLocal(returnUrl);
    }
    else
    {
        // User is new, ask for their desired membership name
        string loginData = OAuthWebSecurity.SerializeProviderUserId(result.Provider, result.ProviderUserId);
        ViewBag.ProviderDisplayName = OAuthWebSecurity.GetOAuthClientData(result.Provider).DisplayName;
        ViewBag.ReturnUrl = returnUrl;
        var client = new FacebookClient(Session["facebooktoken"].ToString());
        dynamic response = client.Get("me", new { fields = "gender, birthday" });
        return View("ExternalLoginConfirmation", 
            new RegisterExternalLoginModel 
            { 
                UserName = result.UserName, 
                FullName = result.ExtraData["name"], 
                DateOfBirth = DateTime.ParseExact(response["birthday"], "MM/dd/yyyy", CultureInfo.InvariantCulture), 
                ExternalLoginData = loginData 
            });
    }
}

我希望有人能告诉我我在这里做错了什么。我已经在谷歌上搜索了两天了，但不知怎么的，我还是没能找到正确的答案。也可能是我太笨了，看不懂。

任何帮助都将是非常感激的。

Erwin

        fbAuthOpt.Scope.Add("email");
        fbAuthOpt.Scope.Add("user_birthday");
        fbAuthOpt.AppId = "";
        fbAuthOpt.AppSecret = "";
        fbAuthOpt.SignInAsAuthenticationType = DefaultAuthenticationTypes.ExternalCookie;
        fbAuthOpt.Provider = new FacebookAuthenticationProvider
        {
            OnAuthenticated = async context =>
            {
                context.Identity.AddClaim(new System.Security.Claims.Claim("FacebookAccessToken", context.AccessToken));
                foreach (var claim in context.User)
                {
                    var claimType = string.Format("urn:facebook:{0}", claim.Key);
                    var claimValue = claim.Value.ToString();
                    if (!context.Identity.HasClaim(claimType, claimValue))
                        context.Identity.AddClaim(new System.Security.Claims.Claim(claimType, claimValue, "XmlSchemaString", "Facebook"));
                }
            }
        };
        app.UseFacebookAuthentication(fbAuthOpt);