使用GSSManager验证Kerberos票证

Question

我有以下代码:

public static void main(String args[]){
    try {
        //String ticket = "Negotiate YIGCBg...==";
        //byte[] kerberosTicket = ticket.getBytes();
        byte[] kerberosTicket = Base64.decode("YIGCBg...==");
        GSSContext context = GSSManager.getInstance().createContext((GSSCredential) null);
        context.acceptSecContext(kerberosTicket, 0, kerberosTicket.length);
        String user = context.getSrcName().toString();
        context.dispose();
    } catch (GSSException e) {
        e.printStackTrace();
    } catch (Base64DecodingException e) {
        e.printStackTrace();
    }
}

当然它失败了.这是例外:

GSSException: Defective token detected (Mechanism level: GSSHeader did not find the right tag)

我不知道我应该做些什么来解决这个问题.老实说,我真的不懂Kerberos.

我通过发送WWW-Authenticate带有"Negotiate" 的适当标题的401 作为值来获得此票.浏览器立即使用authorization包含此票证的标题再次发出相同的请求.

我希望我能验证票证并确定用户是谁.

我需要keytab文件吗？如果是这样,我将在哪个凭据下运行？我正在尝试将Kerberos票证用于网站的身份验证.凭据是否是IIS的凭据？

我错过了什么？

---

更新1 从Michael-O的回复中,我做了一些谷歌搜索并找到了这篇文章,这引导我阅读这篇文章.

上table 3,我发现了1.3.6.1.5.5.2 SPNEGO.

我现在已经按照第一篇文章中的示例添加了我的凭据.这是我的代码:

public static void main(String args[]){
    try {            
        Oid mechOid = new Oid("1.3.6.1.5.5.2");

        GSSManager manager = GSSManager.getInstance();

        GSSCredential myCred = manager.createCredential(null,
                GSSCredential.DEFAULT_LIFETIME,
                mechOid,
                GSSCredential.ACCEPT_ONLY);

        GSSContext context = manager.createContext(myCred);

        byte[] ticket = Base64.decode("YIGCBg...==");
        context.acceptSecContext(ticket, 0, ticket.length);
        String user = context.getSrcName().toString();
        context.dispose();
    } catch (GSSException e) {
        e.printStackTrace();
    } catch (Base64DecodingException e) {
        e.printStackTrace();
    }
}

但是现在代码失败了createCredential,出现了这个错误:

GSSException: No valid credentials provided (Mechanism level: Failed to find any Kerberos credentails)

---

这是整张票: YIGCBgYrBgEFBQKgeDB2oDAwLgYKKwYBBAGCNwICCgYJKoZIgvcSAQICBgkqhkiG9xIBAgIGCisGAQQBgjcCAh6iQgRATlRMTVNTUAABAAAAl7II4g4ADgAyAAAACgAKACgAAAAGAbEdAAAAD0xBUFRPUC0yNDVMSUZFQUNDT1VOVExMQw==

Answer 1

从Java验证SPNEGO票证是一个有点复杂的过程.这是一个简短的概述,但请记住,这个过程可能会有很多陷阱.您真的需要了解Active Directory,Kerberos,SPNEGO和JAAS如何运行以成功诊断问题.

在开始之前,请确保您知道Windows域的kerberos域名.出于这个答案的目的,我会假设它是MYDOMAIN.您可以通过echo %userdnsdomain%从cmd窗口运行来获取领域名称.请注意,kerberos 区分大小写,并且领域几乎总是ALL CAPS.

步骤1 - 获取Kerberos Keytab

为了使kerberos客户端访问服务,它会请求代表该服务的服务主体名称[SPN]的票证.SPN通常源自机器名称和所访问的服务类型(例如HTTP/www.my-domain.com).为了验证特定SPN​​的kerberos票证,您必须拥有一个keytab文件,其中包含Kerberos域控制器[KDC]票证授予票证[TGT]服务和服务提供商(您)都知道的共享密码.

就Active Directory而言,KDC是域控制器,共享密钥只是拥有SPN的帐户的纯文本密码.SPN可以由AD中的计算机或用户对象拥有.

如果要定义服务,在AD中设置SPN的最简单方法是设置基于用户的SPN,如下所示:

1. 在AD中创建一个未被过期的服务帐户,其密码不会过期,例如带密码的SVC_HTTP_MYSERVER ReallyLongRandomPass

2. 使用Windows setspn实用程序将服务SPN绑定到帐户.最佳做法是为主机的短名称和FQDN定义多个SPN:

   setspn -U -S HTTP/myserver@MYDOMAIN SVC_HTTP_MYSERVER
   setspn -U -S HTTP/myserver.my-domain.com@MYDOMAIN SVC_HTTP_MYSERVER
   

3. 使用Java的ktab实用程序为帐户生成密钥表.

   ktab -k FILE:http_myserver.ktab -a HTTP/myserver@MYDOMAIN ReallyLongRandomPass
   ktab -k FILE:http_myserver.ktab -a HTTP/myserver.my-domain.com@MYDOMAIN ReallyLongRandomPass
   

如果您尝试验证绑定到计算机帐户或您无法控制的用户帐户的预先存在的SPN,则上述操作无效.您需要从ActiveDirectory本身提取密钥表.该Wireshark的Kerberos的页面有一些这方面的良好指针.

第2步 - 设置您的krb5.conf

在%JAVA_HOME%/jre/lib/security创建描述您的域的krb5.conf中.确保您在此处定义的领域与您为SPN设置的领域相匹配.如果未将文件放在JVM目录中,则可以通过-Djava.security.krb5.conf=C:\path\to\krb5.conf在命令行上进行设置来指向该文件.

例:

[libdefaults]
  default_realm = MYDOMAIN

[realms]
  MYDOMAIN = {
    kdc = dc1.my-domain.com
    default_domain = my-domain.com
  }

[domain_realm]
  .my-domain.com = MYDOMAIN
  my-domain.com = MYDOMAIN

第3步 - 设置JAAS login.conf

您的JAAS login.conf应定义一个登录配置,将Krb5LoginModule设置为接受器.这是一个假设我们在上面创建的keytab所在的示例C:\http_myserver.ktab.通过-Djava.security.auth.login.config=C:\path\to\login.conf在命令行上设置指向JASS配置文件.

http_myserver_mydomain {
  com.sun.security.auth.module.Krb5LoginModule required
  principal="HTTP/myserver.my-domain.com@MYDOMAIN"
  doNotPrompt="true" 
  useKeyTab="true" 
  keyTab="C:/http_myserver.ktab"
  storeKey="true"
  isInitiator="false";
};

或者,您可以在运行时生成JAAS配置,如下所示:

public static Configuration getJaasKrb5TicketCfg(
    final String principal, final String realm, final File keytab) {
  return new Configuration() {
    @Override
    public AppConfigurationEntry[] getAppConfigurationEntry(String name) {
      Map<String, String> options = new HashMap<String, String>();
      options.put("principal",    principal);
      options.put("keyTab",       keytab.getAbsolutePath());
      options.put("doNotPrompt", "true");
      options.put("useKeyTab",   "true");
      options.put("storeKey",    "true");
      options.put("isInitiator", "false");

      return new AppConfigurationEntry[] {
        new AppConfigurationEntry(
          "com.sun.security.auth.module.Krb5LoginModule",
          LoginModuleControlFlag.REQUIRED, options)
      };
    }
  };
}

您可以为此配置创建一个LoginContext,如下所示:

LoginContext ctx = new LoginContext("doesn't matter", subject, null, 
  getJaasKrbValidationCfg("HTTP/myserver.my-domain.com@MYDOMAIN", "MYDOMAIN", 
    new File("C:/path/to/my.ktab")));

第4步 - 接受机票

这是一个小小的袖手旁观,但一般的想法是定义一个使用票证执行SPNEGO协议的PriviledgedAction.请注意,此示例不检查SPNEGO协议是否完整.例如,如果客户端请求服务器身份验证,则需要返回acceptSecContext()HTTP响应中的身份验证标头中生成的令牌.

public class Krb5TicketValidateAction implements PrivilegedExceptionAction<String> {
  public Krb5TicketValidateAction(byte[] ticket, String spn) {
    this.ticket = ticket;
    this.spn = spn;
  }

  @Override
  public String run() throws Exception {
    final Oid spnegoOid = new Oid("1.3.6.1.5.5.2");

    GSSManager gssmgr = GSSManager.getInstance();

    // tell the GSSManager the Kerberos name of the service
    GSSName serviceName = gssmgr.createName(this.spn, GSSName.NT_USER_NAME);

    // get the service's credentials. note that this run() method was called by Subject.doAs(),
    // so the service's credentials (Service Principal Name and password) are already 
    // available in the Subject
    GSSCredential serviceCredentials = gssmgr.createCredential(serviceName,
      GSSCredential.INDEFINITE_LIFETIME, spnegoOid, GSSCredential.ACCEPT_ONLY);

    // create a security context for decrypting the service ticket
    GSSContext gssContext = gssmgr.createContext(serviceCredentials);

    // decrypt the service ticket
    System.out.println("Entering accpetSecContext...");
    gssContext.acceptSecContext(this.ticket, 0, this.ticket.length);

    // get the client name from the decrypted service ticket
    // note that Active Directory created the service ticket, so we can trust it
    String clientName = gssContext.getSrcName().toString();

    // clean up the context
    gssContext.dispose();

    // return the authenticated client name
    return clientName;
  }

  private final byte[] ticket;
  private final String spn;
}

然后,要验证票证,您将执行以下操作.假设它ticket包含来自身份验证标头的已经基于64位解码的票证.如果格式为,spn则应从HostHTTP请求中的标头派生HTTP/<HOST>@<REALM>.例如,如果Host标题是myserver.my-domain.com那么spn应该是HTTP/myserver.my-domain.com@MYDOMAIN.

public boolean isTicketValid(String spn, byte[] ticket) {
  LoginContext ctx = null;
  try {
    // this is the name from login.conf.  This could also be a parameter
    String ctxName = "http_myserver_mydomain";

    // define the principal who will validate the ticket
    Principal principal = new KerberosPrincipal(spn, KerberosPrincipal.KRB_NT_SRV_INST);
    Set<Principal> principals = new HashSet<Principal>();
    principals.add(principal);

    // define the subject to execute our secure action as
    Subject subject = new Subject(false, principals, new HashSet<Object>(), 
      new HashSet<Object>());

    // login the subject
    ctx = new LoginContext("http_myserver_mydomain", subject);
    ctx.login();

    // create a validator for the ticket and execute it
    Krb5TicketValidateAction validateAction = new Krb5TicketValidateAction(ticket, spn);
    String username = Subject.doAs(subject, validateAction);
    System.out.println("Validated service ticket for user " + username 
      + " to access service " + spn );
    return true;
  } catch(PriviledgedActionException e ) {
     System.out.println("Invalid ticket for " + spn + ": " + e);
  } catch(LoginException e) {
    System.out.println("Error creating validation LoginContext for " 
      + spn + ": " + e);
  } finally {
    try {
      if(ctx!=null) { ctx.logout(); }
    } catch(LoginException e) { /* noop */ }
  }

  return false;
}

Answer 2

这不是Kerberos票证,而是SPNEGO票证.您的上下文有错误的机制.

编辑:虽然,您现在拥有正确的机制,但您的客户端正在向您发送GSL-API无法处理的NTLM令牌.使用Base 64令牌,解码为原始字节并显示ASCII字符.如果它开始NTLMSSP,它将无法确定并且您已经破坏了Kerberos设置.

编辑2:这是你的票:

60 81 82 06 06 2B 06 01 05 05 02 A0 78 30 76 A0 30 30 2E 06  `..+..... x0v 00..
0A 2B 06 01 04 01 82 37 02 02 0A 06 09 2A 86 48 82 F7 12 01  .+....7.....*H÷..
02 02 06 09 2A 86 48 86 F7 12 01 02 02 06 0A 2B 06 01 04 01  ....*H÷......+....
82 37 02 02 1E A2 42 04 40 4E 54 4C 4D 53 53 50 00 01 00 00  7...¢B.@NTLMSSP....
00 97 B2 08 E2 0E 00 0E 00 32 00 00 00 0A 00 0A 00 28 00 00  .².â....2.......(..
00 06 01 B1 1D 00 00 00 0F 4C 41 50 54 4F 50 2D 32 34 35 4C  ...±.....LAPTOP-245L
49 46 45 41 43 43 4F 55 4E 54 4C 4C 43                       IFEACCOUNTLLC       

这是SPNEGO令牌中的包装NTLM令牌.这仅仅意味着Kerberos由于某些原因而失败,例如,

• SPN未注册
• 时钟偏移
• 不允许使用Kerberos
• DNS记录不正确

最好的选择是在客户端上使用Wireshark来查找根本原因.

请注意,Java并没有支持NTLM的SPNEGO submechanism.NTLM仅由SSPI和Heimdal支持.