如何在dotnet核心中访问标识中的扩展属性

using Microsoft.AspNetCore.Identity;

// 定义扩展属性
public class ApplicationUser : IdentityUser
{
    [PersonalData]
    public string FullName { get; set; }
}

// 访问扩展属性
public class SomeService
{
    private readonly UserManager<ApplicationUser> _userManager;

    public SomeService(UserManager<ApplicationUser> userManager)
    {
        _userManager = userManager;
    }

    public string GetFullName(string userId)
    {
        var user = _userManager.FindByIdAsync(userId).Result;
        var fullName = user.FindFirstValue("FullName");
        return fullName;
    }
}