ASP.NET Core 3.1浏览器嗅探如何解决部分浏览器丢失Cookie问题

看了前文的同学们应该都知道，搜狗、360等浏览器在单点登录中反复重定向，最终失败报错。

原因在于，非Chrome80+浏览器不识别Cookie上的SameSite=none属性值,导致认证Cookie在后续请求中被抛弃。

截至2020/3/30号,非Chrome浏览器测试包含两种结果：

• case1：可设置cookie的samesite=none， 浏览器可读取该cookie
• case2：对cookie设置samesite=none， 浏览器不能读取该cookie

嗯，我之前报的360急速浏览器在新版已经更新了Chrome内核，作为主流的搜狗和猎豹浏览器还是使用旧版本Chrome内核，这是要闹哪样？

如果Web应用程序打算支持旧内核浏览器，则需要实现浏览器嗅探。ASP.NET Core不会帮你实现浏览器嗅探，因为User-Agents值易变且经常更改。

但是Microsoft.AspNetCore.CookiePolicy中的扩展点允许插入浏览器嗅探逻辑。

在Startup.Configure中，在调用UseAuthentication或任何写入cookie的方法之前添加调用UseCookiePolicy的代码：

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseExceptionHandler("/Error");
        app.UseHsts();
    }

    app.UseHttpsRedirection();
    app.UseStaticFiles();

    app.UseRouting();
  // 表示ASP.NET Core 启动Cookie策略
    app.UseCookiePolicy();
    app.UseAuthentication();
    app.UseAuthorization();

    app.UseEndpoints(endpoints =>
    {
        endpoints.MapRazorPages();
    });
}

在Startup.ConfigureServices, 添加Cookie的策略配置代码：

public void ConfigureServices(IServiceCollection services)
{
    services.Configure(options =>
    {
        options.MinimumSameSitePolicy = (SameSiteMode)(-1);
        options.OnAppendCookie = cookieContext =>
            CheckSameSite(cookieContext.Context, cookieContext.CookieOptions);
        options.OnDeleteCookie = cookieContext =>
            CheckSameSite(cookieContext.Context, cookieContext.CookieOptions);
    });

    services.AddRazorPages();
}

private void CheckSameSite(HttpContext httpContext, CookieOptions options)
{
    if (options.SameSite == SameSiteMode.None)
    {
        var userAgent = httpContext.Request.Headers["User-Agent"].ToString();
        if (MyUserAgentDetectionLib.DisallowsSameSiteNone(userAgent))
        {
            options.SameSite = SameSiteMode.Unspecified;
        }

    }
}

上面的例子中，MyUserAgentDetectionLib.DisallowsSameSiteNone 是一个自定义的库文件，侦测不支持SameSite=None的UserAgent。

ASP.NET Core3.1 对与SameSiteMode新增了一个 Unspecified枚举值，表示服务端不会对Cookie设置SameSite属性值， 后面的携带Cookie的事情交给浏览器默认配置。

具体的侦测代码如下：

public static bool DisallowsSameSiteNone(string userAgent)
{
    // Check if a null or empty string has been passed in, since this
    // will cause further interrogation of the useragent to fail.
     if (String.IsNullOrWhiteSpace(userAgent))
        return false;
    
    // Cover all iOS based browsers here. This includes:
    // - Safari on iOS 12 for iPhone, iPod Touch, iPad
    // - WkWebview on iOS 12 for iPhone, iPod Touch, iPad
    // - Chrome on iOS 12 for iPhone, iPod Touch, iPad
    // All of which are broken by SameSite=None, because they use the iOS networking
    // stack.
    if (userAgent.Contains("CPU iPhone OS 12") ||
        userAgent.Contains("iPad; CPU OS 12"))
    {
        return true;
    }

    // Cover Mac OS X based browsers that use the Mac OS networking stack.
    // This includes:
    // - Safari on Mac OS X.
    // This does not include:
    // - Chrome on Mac OS X
    // Because they do not use the Mac OS networking stack.
    if (userAgent.Contains("Macintosh; Intel Mac OS X 10_14") &&
        userAgent.Contains("Version/") && userAgent.Contains("Safari"))
    {
        return true;
    }

    // Cover Chrome 50-69, because some versions are broken by SameSite=None,
    // and none in this range require it.
    // Note: this covers some pre-Chromium Edge versions,
    // but pre-Chromium Edge does not require SameSite=None.
    if (userAgent.Contains("Chrome/5") || userAgent.Contains("Chrome/6"))
    {
        return true;
    }

    return false;
}