Blazor 服务器应用程序可以在用户第一次成功身份验证后触发 OnAuthorizedAsync 方法。您可以在 Blazor 服务器应用程序的 Startup.cs 文件中添加以下代码：

public void ConfigureServices(IServiceCollection services)
{
    services.AddRazorPages();
    services.AddServerSideBlazor();
    services.AddScoped();
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    //...

    app.UseAuthentication();

    //...
}

public class CustomAuthenticationStateProvider : AuthenticationStateProvider
{
    private readonly IHttpContextAccessor _httpContextAccessor;

    public CustomAuthenticationStateProvider(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor;
    }

    public override async Task GetAuthenticationStateAsync()
    {
        var authState = await base.GetAuthenticationStateAsync();

        if (authState.User.Identity.IsAuthenticated)
        {
            var claim = authState.User.FindFirst("urn:nhs:profile:id");
            if (claim != null)
            {
                // get user ID and set it to session
                var userId = claim.Value;
                var httpContext = _httpContextAccessor.HttpContext;
                httpContext.Session.SetString("UserId", userId);
                bool isFirstLogin = /* check if the user logged in first time */;
                if (isFirstLogin)
                {
                    // do something when the user logs in for the first time
                }
            }
        }

        return authState;
    }
}

在上面的代码中，我们使用 CustomAuthenticationStateProvider 类来扩展 AuthenticationStateProvider，并在 GetAuthenticationStateAsync 方法中访问 HttpContext 和 Session 对象以获取用户 ID 并将其保存在会话中。接下来，我们可以检查用户是否第一次登录，并执行相应的操作。例如，在这里，我们将其设置为 bool 类型的 isFirstLogin 变量，在后续的代码中使用它来检查并执行操作。