问如何从具有ASP.Net核心身份的登录用户中检索Facebook配置文件图片？

EN

    public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        //...
        app.UseFacebookAuthentication(new FacebookOptions
        {
            AuthenticationScheme = "Facebook",
            AppId = Configuration["ExternalLoginProviders:Facebook:AppId"],
            AppSecret = Configuration["ExternalLoginProviders:Facebook:AppSecret"]
        });
    }

    [HttpGet]
    [AllowAnonymous]
    public async Task<IActionResult> ExternalLoginCallback(string returnUrl = null, string remoteError = null)
    {
        //... SignInManager<User> _signInManager; declared before
        ExternalLoginInfo info = await _signInManager.GetExternalLoginInfoAsync();
        SignInResult signInResult = await _signInManager.ExternalLoginSignInAsync(info.LoginProvider, info.ProviderKey, isPersistent: false);

        byte[] thumbnailBytes = null;

        if (info.LoginProvider == "Facebook")
        {
            string nameIdentifier = info.Principal.FindFirstValue(ClaimTypes.NameIdentifier);
            string thumbnailUrl = $"https://graph.facebook.com/{nameIdentifier}/picture?type=large";
            using (HttpClient httpClient = new HttpClient())
            {
                thumbnailBytes = await httpClient.GetByteArrayAsync(thumbnailUrl);
            }
        }
        //...
    }