ASP.NET Cookie是怎么生成的

01/24 16:20
阅读数 4

ASP.NET Cookie是怎么生成的

可能有人知道Cookie的生成由machineKey有关,machineKey用于决定Cookie生成的算法和密钥,并如果使用多台服务器做负载均衡时,必须指定一致的machineKey用于解密,那么这个过程到底是怎样的呢?

如果需要在.NET Core中使用ASP.NET Cookie,本文将提到的内容也将是一些必经之路。

抽丝剥茧,一步一步分析

首先用户通过AccountController->Login进行登录:

//
// POST: /Account/Login
public async Task<ActionResult> Login(LoginViewModel model, string returnUrl)
{
    if (!ModelState.IsValid)
    {
        return View(model);
    }

    var result = await SignInManager.PasswordSignInAsync(model.Email, model.Password, model.RememberMe, shouldLockout: false);
    switch (result)
    {
        case SignInStatus.Success:
            return RedirectToLocal(returnUrl);
        // ......省略其它代码
    }
}

它调用了SignInManagerPasswordSignInAsync方法,该方法代码如下(有删减):

public virtual async Task<SignInStatus> PasswordSignInAsync(string userName, string password, bool isPersistent, bool shouldLockout)
{
    // ...省略其它代码
    if (await UserManager.CheckPasswordAsync(user, password).WithCurrentCulture())
    {
        if (!await IsTwoFactorEnabled(user))
        {
            await UserManager.ResetAccessFailedCountAsync(user.Id).WithCurrentCulture();
        }
        return await SignInOrTwoFactor(user, isPersistent).WithCurrentCulture();
    }
    // ...省略其它代码
    return SignInStatus.Failure;
}

想浏览原始代码,可参见官方的Github链接:https://github.com/aspnet/AspNetIdentity/blob/master/src/Microsoft.AspNet.Identity.Owin/SignInManager.cs#L235-L276

可见它先需要验证密码,密码验证正确后,它调用了SignInOrTwoFactor方法,该方法代码如下:

private async Task<SignInStatus> SignInOrTwoFactor(TUser user, bool isPersistent)
{
    var id = Convert.ToString(user.Id);
    if (await IsTwoFactorEnabled(user) && !await AuthenticationManager.TwoFactorBrowserRememberedAsync(id).WithCurrentCulture())
    {
        var identity = new ClaimsIdentity(DefaultAuthenticationTypes.TwoFactorCookie);
        identity.AddClaim(new Claim(ClaimTypes.NameIdentifier, id));
        AuthenticationManager.SignIn(identity);
        return SignInStatus.RequiresVerification;
    }
    await SignInAsync(user, isPersistent, false).WithCurrentCulture();
    return SignInStatus.Success;
}

该代码只是判断了是否需要做双重验证,在需要双重验证的情况下,它调用了AuthenticationManagerSignIn方法;否则调用SignInAsync方法。SignInAsync的源代码如下:

public virtual async Task SignInAsync(TUser user, bool isPersistent, bool rememberBrowser)
{
    var userIdentity = await CreateUserIdentityAsync(user).WithCurrentCulture();
    // Clear any partial cookies from external or two factor partial sign ins
    AuthenticationManager.SignOut(DefaultAuthenticationTypes.ExternalCookie, DefaultAuthenticationTypes.TwoFactorCookie);
    if (rememberBrowser)
    {
        var rememberBrowserIdentity = AuthenticationManager.CreateTwoFactorRememberBrowserIdentity(ConvertIdToString(user.Id));
        AuthenticationManager.SignIn(new AuthenticationProperties { IsPersistent = isPersistent }, userIdentity, rememberBrowserIdentity);
    }
    else
    {
        AuthenticationManager.SignIn(new AuthenticationProperties { IsPersistent = isPersistent }, userIdentity);
    }
}

可见,最终所有的代码都是调用了AuthenticationManager.SignIn方法,所以该方法是创建Cookie的关键。

AuthenticationManager的实现定义在Microsoft.Owin中,因此无法在ASP.NET Identity中找到其源代码,因此我们打开Microsoft.Owin的源代码继续跟踪(有删减):

public void SignIn(AuthenticationProperties properties, params ClaimsIdentity[] identities)
{
    AuthenticationResponseRevoke priorRevoke = AuthenticationResponseRevoke;
    if (priorRevoke != null)
    {
        // ...省略不相关代码
        AuthenticationResponseRevoke = new AuthenticationResponseRevoke(filteredSignOuts);
    }

    AuthenticationResponseGrant priorGrant = AuthenticationResponseGrant;
    if (priorGrant == null)
    {
        AuthenticationResponseGrant = new AuthenticationResponseGrant(new ClaimsPrincipal(identities), properties);
    }
    else
    {
        // ...省略不相关代码

        AuthenticationResponseGrant = new AuthenticationResponseGrant(new ClaimsPrincipal(mergedIdentities), priorGrant.Properties);
    }
}

AuthenticationManagerGithub链接如下:https://github.com/aspnet/AspNetKatana/blob/c33569969e79afd9fb4ec2d6bdff877e376821b2/src/Microsoft.Owin/Security/AuthenticationManager.cs

可见它用到了AuthenticationResponseGrant,继续跟踪可以看到它实际是一个属性:

public AuthenticationResponseGrant AuthenticationResponseGrant
{
    // 省略get
    set
    {
        if (value == null)
        {
            SignInEntry = null;
        }
        else
        {
            SignInEntry = Tuple.Create((IPrincipal)value.Principal, value.Properties.Dictionary);
        }
    }
}

发现它其实是设置了SignInEntry,继续追踪:

public Tuple<IPrincipal, IDictionary<string, string>> SignInEntry
{
    get { return _context.Get<Tuple<IPrincipal, IDictionary<string, string>>>(OwinConstants.Security.SignIn); }
    set { _context.Set(OwinConstants.Security.SignIn, value); }
}

其中,_context的类型为IOwinContextOwinConstants.Security.SignIn的常量值为"security.SignIn"

跟踪完毕……

啥?跟踪这么久,居然跟丢啦!?

当然没有!但接下来就需要一定的技巧了。

原来,ASP.NET是一种中间件(Middleware)模型,在这个例子中,它会先处理MVC中间件,该中间件处理流程到设置AuthenticationResponseGrant/SignInEntry为止。但接下来会继续执行CookieAuthentication中间件,该中间件的核心代码在aspnet/AspNetKatana仓库中可以看到,关键类是CookieAuthenticationHandler,核心代码如下:

protected override async Task ApplyResponseGrantAsync()
{
    AuthenticationResponseGrant signin = Helper.LookupSignIn(Options.AuthenticationType);
    // ... 省略部分代码

    if (shouldSignin)
    {
        var signInContext = new CookieResponseSignInContext(
            Context,
            Options,
            Options.AuthenticationType,
            signin.Identity,
            signin.Properties,
            cookieOptions);

        // ... 省略部分代码

        model = new AuthenticationTicket(signInContext.Identity, signInContext.Properties);
        // ... 省略部分代码

        string cookieValue = Options.TicketDataFormat.Protect(model);

        Options.CookieManager.AppendResponseCookie(
            Context,
            Options.CookieName,
            cookieValue,
            signInContext.CookieOptions);
    }
    // ... 又省略部分代码
}

这个原始函数有超过200行代码,这里我省略了较多,但保留了关键、核心部分,想查阅原始代码可以移步Github链接:https://github.com/aspnet/AspNetKatana/blob/0fc4611e8b04b73f4e6bd68263e3f90e1adfa447/src/Microsoft.Owin.Security.Cookies/CookieAuthenticationHandler.cs#L130-L313

这里挑几点最重要的讲。

MVC建立关系

建立关系的核心代码就是第一行,它从上文中提到的位置取回了AuthenticationResponseGrant,该Grant保存了ClaimsAuthenticationTicketCookie重要组成部分:

AuthenticationResponseGrant signin = Helper.LookupSignIn(Options.AuthenticationType);

继续查阅LookupSignIn源代码,可看到,它就是从上文中的AuthenticationManager中取回了AuthenticationResponseGrant(有删减):

public AuthenticationResponseGrant LookupSignIn(string authenticationType)
{
    // ...
    AuthenticationResponseGrant grant = _context.Authentication.AuthenticationResponseGrant;
    // ...

    foreach (var claimsIdentity in grant.Principal.Identities)
    {
        if (string.Equals(authenticationType, claimsIdentity.AuthenticationType, StringComparison.Ordinal))
        {
            return new AuthenticationResponseGrant(claimsIdentity, grant.Properties ?? new AuthenticationProperties());
        }
    }

    return null;
}

如此一来,柳暗花明又一村,所有的线索就立即又明朗了

Cookie的生成

AuthenticationTicket变成Cookie字节串,最关键的一步在这里:

string cookieValue = Options.TicketDataFormat.Protect(model);

在接下来的代码中,只提到使用CookieManager将该Cookie字节串添加到Http响应中,翻阅CookieManager可以看到如下代码:

public void AppendResponseCookie(IOwinContext context, string key, string value, CookieOptions options)
{
    if (context == null)
    {
        throw new ArgumentNullException("context");
    }
    if (options == null)
    {
        throw new ArgumentNullException("options");
    }

    IHeaderDictionary responseHeaders = context.Response.Headers;
    // 省去“1万”行计算chunk和处理细节的流程
    responseHeaders.AppendValues(Constants.Headers.SetCookie, chunks);
}

有兴趣的朋友可以访问Github看原始版本的代码:https://github.com/aspnet/AspNetKatana/blob/0fc4611e8b04b73f4e6bd68263e3f90e1adfa447/src/Microsoft.Owin/Infrastructure/ChunkingCookieManager.cs#L125-L215

可见这个实现比较……简单,就是往Response.Headers中加了个头,重点只要看TicketDataFormat.Protect方法即可。

逐渐明朗

该方法源代码如下:

public string Protect(TData data)
{
    byte[] userData = _serializer.Serialize(data);
    byte[] protectedData = _protector.Protect(userData);
    string protectedText = _encoder.Encode(protectedData);
    return protectedText;
}

可见它依赖于_serializer_protector_encoder三个类,其中,_serializer的关键代码如下:

public virtual byte[] Serialize(AuthenticationTicket model)
{
    using (var memory = new MemoryStream())
    {
        using (var compression = new GZipStream(memory, CompressionLevel.Optimal))
        {
            using (var writer = new BinaryWriter(compression))
            {
                Write(writer, model);
            }
        }
        return memory.ToArray();
    }
}

其本质是进行了一次二进制序列化,并紧接着进行了gzip压缩,确保Cookie大小不要失去控制(因为.NET的二进制序列化结果较大,并且微软喜欢搞xml,更大😂)。

然后来看一下_encoder源代码:

public string Encode(byte[] data)
{
    if (data == null)
    {
        throw new ArgumentNullException("data");
    }

    return Convert.ToBase64String(data).TrimEnd('=').Replace('+', '-').Replace('/', '_');
}

可见就是进行了一次简单的base64-url编码,注意该编码把=号删掉了,所以在base64-url解码时,需要补=号。

这两个都比较简单,稍复杂的是_protector,它的类型是IDataProtector

IDataProtector

它在CookieAuthenticationMiddleware中进行了初始化,创建代码和参数如下:

IDataProtector dataProtector = app.CreateDataProtector(
    typeof(CookieAuthenticationMiddleware).FullName,
    Options.AuthenticationType, "v1");

注意它传了三个参数,第一个参数是CookieAuthenticationMiddlewareFullName,也就是"Microsoft.Owin.Security.Cookies.CookieAuthenticationMiddleware",第二个参数如果没定义,默认值是CookieAuthenticationDefaults.AuthenticationType,该值为定义为"Cookies"

但是,在默认创建的ASP.NET MVC模板项目中,该值被重新定义为ASP.NET Identity的默认值,即"ApplicationCookie",需要注意。

然后来看看CreateDataProtector的源码:

public static IDataProtector CreateDataProtector(this IAppBuilder app, params string[] purposes)
{
    if (app == null)
    {
        throw new ArgumentNullException("app");
    }

    IDataProtectionProvider dataProtectionProvider = GetDataProtectionProvider(app);
    if (dataProtectionProvider == null)
    {
        dataProtectionProvider = FallbackDataProtectionProvider(app);
    }
    return dataProtectionProvider.Create(purposes);
}

public static IDataProtectionProvider GetDataProtectionProvider(this IAppBuilder app)
{
    if (app == null)
    {
        throw new ArgumentNullException("app");
    }
    object value;
    if (app.Properties.TryGetValue("security.DataProtectionProvider", out value))
    {
        var del = value as DataProtectionProviderDelegate;
        if (del != null)
        {
            return new CallDataProtectionProvider(del);
        }
    }
    return null;
}

可见它先从IAppBuilder"security.DataProtectionProvider"属性中取一个IDataProtectionProvider,否则使用DpapiDataProtectionProvider

我们翻阅代码,在OwinAppContext中可以看到,该值被指定为MachineKeyDataProtectionProvider

builder.Properties[Constants.SecurityDataProtectionProvider] = new MachineKeyDataProtectionProvider().ToOwinFunction();

文中的Constants.SecurityDataProtectionProvider,刚好就被定义为"security.DataProtectionProvider"

我们翻阅MachineKeyDataProtector的源代码,刚好看到它依赖于MachineKey

internal class MachineKeyDataProtector
{
    private readonly string[] _purposes;

    public MachineKeyDataProtector(params string[] purposes)
    {
        _purposes = purposes;
    }

    public virtual byte[] Protect(byte[] userData)
    {
        return MachineKey.Protect(userData, _purposes);
    }

    public virtual byte[] Unprotect(byte[] protectedData)
    {
        return MachineKey.Unprotect(protectedData, _purposes);
    }
}

最终到了我们的老朋友MachineKey

逆推过程,破解Cookie

首先总结一下这个过程,对一个请求在Mvc中的流程来说,这些代码集中在ASP.NET Identity中,它会经过:

  1. AccountController
  2. SignInManager
  3. AuthenticationManager
  4. 设置AuthenticationResponseGrant

然后进入CookieAuthentication的流程,这些代码集中在Owin中,它会经过:

  1. CookieAuthenticationMiddleware(读取AuthenticationResponseGrant
  2. ISecureDataFormat(实现类:SecureDataFormat<T>
  3. IDataSerializer(实现类:TicketSerializer
  4. IDataProtector(实现类:MachineKeyDataProtector
  5. ITextEncoder(实现类:Base64UrlTextEncoder

这些过程,结果上文中找到的所有参数的值,我总结出的“祖传破解代码”如下:

string cookie = "nZBqV1M-Az7yJezhb6dUzS_urj1urB0GDufSvDJSa0pv27CnDsLHRzMDdpU039j6ApL-VNfrJULfE85yU9RFzGV_aAGXHVkGckYqkCRJUKWV8SqPEjNJ5ciVzW--uxsCBNlG9jOhJI1FJIByRzYJvidjTYABWFQnSSd7XpQRjY4lb082nDZ5lwJVK3gaC_zt6H5Z1k0lUFZRb6afF52laMc___7BdZ0mZSA2kRxTk1QY8h2gQh07HqlR_p0uwTFNKi0vW9NxkplbB8zfKbfzDj7usep3zAeDEnwofyJERtboXgV9gIS21fLjc58O-4rR362IcCi2pYjaKHwZoO4LKWe1bS4r1tyzW0Ms-39Njtiyp7lRTN4HUHMUi9PxacRNgVzkfK3msTA6LkCJA3VwRm_UUeC448Lx5pkcCPCB3lGat_5ttGRjKD_lllI-YE4esXHB5eJilJDIZlEcHLv9jYhTl17H0Jl_H3FqXyPQJR-ylQfh";
var bytes = TextEncodings.Base64Url.Decode(cookie);
var decrypted = MachineKey.Unprotect(bytes,
    "Microsoft.Owin.Security.Cookies.CookieAuthenticationMiddleware",
    "ApplicationCookie",
    "v1");
var serializer = new TicketSerializer();
var ticket = serializer.Deserialize(decrypted);
ticket.Dump(); // Dump为LINQPad专有函数,用于方便调试显示,此处可以用循环输出代替

运行前请设置好app.config/web.config中的machineKey节点,并安装NuGet包:Microsoft.Owin.Security,运行结果如下(完美破解):

总结

学习方式有很多种,其中看代码是我个人非常喜欢的一种方式,并非所有代码都会一马平川。像这个例子可能还需要有一定ASP.NET知识背景。

注意这个“祖传代码”是基于.NET Framework,由于其用到了MachineKey,因此无法在.NET Core中运行。我稍后将继续深入聊聊MachineKey这个类,看它底层代码是如何工作的,然后最终得以在.NET Core中直接破解ASP.NET Identity中的Cookie,敬请期待!

喜欢的朋友请关注我的微信公众号:【DotNet骚操作】

DotNet骚操作

最后,在新的一年里,祝大家阖家欢乐,鼠年大吉!

原文出处:https://www.cnblogs.com/sdflysha/p/20200123-how-does-aspnet-identity-cookie-generated.html

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