CAS 源码分析 （非proxy模式）

 

一、CAS 基本原理   （3，4，5，9.2，9.3是主要步骤）

第一次访问：
1. 浏览器   发起访问WebAPP 请求:  http://www.web.com/app
2. 客户端  AuthenticationFilter Filter 发现Session中无 Assertion,且URL中无 ticket 变量。生成 service url 变量，并重定向到：  https://www.cas-server.com/cas/login?service=http://www.web.com/app



3. CAS server  生成 Login ticket， service 对象，并展示 login 页面，默认提供 username / password 给用户验证。
4. CAS server 端，用户输入 username / password 验证，若通过则生成TGT，存入服务器段（默认为 Map 类型的 cache），同时将TGT id 作为 content创建 cookie 并发送到浏览器。
5. CAS server 端通过TGT 生成service ticket.  重定向到 http://www.web.com/app?ticket=ST-xxx

 

 

6. 客户端   访问 http://www.web.com/app?ticket=ST-xxx
7. 客户端   AuthenticationFilter Filter 发现URL中有 ticket, 跳过 AuthenticationFilter过滤器，到达 Cas20ProxyReceivingTicketValidationFilter过滤器。


8. 客户端 生成验证 service url:  http://www.web.com/app
9. 客户端   Cas20ProxyReceivingTicketValidationFilter 过滤器，使用6处的ticket 与8处的 service 作为参数验证。

  9.1  客户端 生成验证 servlet: https://www.cas-server.com/cas/serviceValidate?ticket=ST-xxx&service=http://www.web.com/app
  9.2  客户端 通过HttpClient访问 9.1 的 url
                注：AbstractUrlBasedTicketValidator.java line 207，如果是用CAS ptotocol验证，则第二个参数 ticket无用。
                得到如下形式的 response:

546 <cas:serviceResponse xmlns:cas='http://www.yale.edu/tp/cas'>
547         <cas:authenticationSuccess>
548                 <cas:user>jack</cas:user>
549
550
551         </cas:authenticationSuccess>
552 </cas:serviceResponse>

   9.3  客户端 解析 response 字符串，生成 assertion (包含 username, validate info 等)

   9.4  客户端 设置 assertion 为 request 的 _const_cas_assertion_ 属性，同时会将assertion记录到session 中去。

   9.5  客户端 如果设置了重定向属性，则重定向到 http://www.web.com/app  --  转步骤10

              否则继续执行以后的 filter，通过servlet 访问 http://www.web.com/app 服务，结束CAS的验证。

 

用户已成功登录，非第一次访问：

10. 客户端 通过重定向访问 http://www.web.com/app

11. 客户端 AuthenticationFilter Filter 发现 session 中有Assertion， 结束本过滤器，转移到下一个过滤器 Cas20ProxyReceivingTicketValidationFilter.

12. 客户段 Cas20ProxyReceivingTicketValidationFilter 发现 本次访问的URL 无 ticket，结束本次过滤，转移到下一个过滤器，继续执行以后的 filter，通过servlet 访问 http://www.web.com/app 服务。

 

二 源码解析

 

1. 客户端 web.xml  片段：

 

...

<filter>
          <filter-name>CAS Authentication Filter</filter-name>
          <filter-class>org.jasig.cas.client.authentication.AuthenticationFilter</filter-class>
          <init-param>
                <param-name>casServerLoginUrl</param-name>
                <param-value>https://www.colorcc.com:8443/cas/login</param-value>
          </init-param>
          <init-param>
                <param-name>serverName</param-name>
                <param-value>http://localhost:8080</param-value>
          </init-param>
    </filter>
    <filter>
          <filter-name>CAS Validation Filter</filter-name>
          <filter-class>org.jasig.cas.client.validation.Cas20ProxyReceivingTicketValidationFilter</filter-class>
          <init-param>
                <param-name>casServerUrlPrefix</param-name>
                <param-value>https://www.colorcc.com:8443/cas</param-value>
          </init-param>
          <init-param>
                <param-name>serverName</param-name>
                <param-value>http://localhost:8080</param-value>
          </init-param>
    <!--   <init-param>
                <param-name>redirectAfterValidation</param-name>
                <param-value>false</param-value>
          </init-param> -->
    </filter>

    <filter-mapping>
        <filter-name>CAS Authentication Filter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
    <filter-mapping>
        <filter-name>CAS Validation Filter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
...

 

2.  AuthenticationFilter 代码:

public final void doFilter(final ServletRequest servletRequest, final ServletResponse servletResponse, final FilterChain filterChain) throws IOException, ServletException {
        final HttpServletRequest request = (HttpServletRequest) servletRequest;
        final HttpServletResponse response = (HttpServletResponse) servletResponse;
        final HttpSession session = request.getSession(false);
        final Assertion assertion = session != null ? (Assertion) session.getAttribute(CONST_CAS_ASSERTION) : null;
        // 如果 session 中有 assertion，则结束 authentication 过滤器，直接跳到下一个过滤器
        if (assertion != null) {
            filterChain.doFilter(request, response);
            return;
        }

        //  2.1 如果 session 中无 assertion, 则构造 service,  如 http://www.web.com/a1
       <strong> final String serviceUrl = constructServiceUrl(request, response);</strong>





        final String ticket = CommonUtils.safeGetParameter(request,getArtifactParameterName());
        final boolean wasGatewayed = this.gatewayStorage.hasGatewayedAlready(request, serviceUrl);

        // 如果 request 中有 ticke变量，则结束本过滤器，直接跳到下一个过滤器
        if (CommonUtils.isNotBlank(ticket) || wasGatewayed) {
            filterChain.doFilter(request, response);
            return;
        }

        final String modifiedServiceUrl;

        log.debug("no ticket and no assertion found");
        if (this.gateway) {
            log.debug("setting gateway attribute in session");
            modifiedServiceUrl = this.gatewayStorage.storeGatewayInformation(request, serviceUrl);
        } else {
            modifiedServiceUrl = serviceUrl;

        }

        if (log.isDebugEnabled()) {
            log.debug("Constructed service url: " + modifiedServiceUrl);
        }

        // 2.2 否 则构造重定向 URL， 其中 casServerLoginUrl 为 web.xml 中 filter 配 置，eg: https://www.cas-server.com/cas/login?service=http://www.web.com/a1
       final String urlToRedirectTo = CommonUtils.constructRedirectUrl(this.casServerLoginUrl, getServiceParameterName(), modifiedServiceUrl, this.renew, this.gateway);


        if (log.isDebugEnabled()) {
            log.debug("redirecting to \"" + urlToRedirectTo + "\"");
        }

        //  2.3 重定向到 CAS server
        response.sendRedirect(urlToRedirectTo);<em>
</em>





    }

  2.1 构造 service url:    http://www.web.com/a1

protected final String constructServiceUrl(final HttpServletRequest request, final HttpServletResponse response) {
        return CommonUtils.constructServiceUrl(request, response, this.service, this.serverName, this.artifactParameterName, this.encodeServiceUrl);
    }

 

3. 重定向URL：  https://www.cas-server.com/cas/login?service=http://www.web.com/a1, 其中 cas server的 web.xml：

<servlet>
    <servlet-name>cas</servlet-name>
    <servlet-class>
      org.jasig.cas.web.init.SafeDispatcherServlet
    </servlet-class>
    <init-param>
      <param-name>publishContext</param-name>
      <param-value>false</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>

  <servlet-mapping>
    <servlet-name>cas</servlet-name>
    <url-pattern>/login</url-pattern>
  </servlet-mapping>

 

     3.1  SafeDispatcherServlet 使用 Spring DispatcherServlet 作为 delegate

 

public final class SafeDispatcherServlet extends HttpServlet {

    // 定义 Spring DispatcherServlet 作为 delegate
    private DispatcherServlet delegate = new DispatcherServlet();

    // 使用 delegate 初始化 servlet
    public void init(final ServletConfig config) {
        try {
            this.delegate.init(config);

        } catch (final Throwable t) {
         ...

     // 使用 delegate 的 service 执行 web 操作
     public void service(final ServletRequest req, final ServletResponse resp)
        throws ServletException, IOException {
        if (this.initSuccess) {
            this.delegate.service(req, resp);
        } else {
            throw new ApplicationContextException(
                "Unable to initialize application context.");
        }
    }

 

    3.2 cas-servlet.xml 配置文件如下, 可以看到 login 对应的 webflow 为： login-webflow.xml

 

<webflow:flow-registry id="flowRegistry" flow-builder-services="builder">
  <webflow:flow-location path="/WEB-INF/login-webflow.xml" id="login"/>
</webflow:flow-registry>

    3.3  根据 login-webflow.xml 配置文件(结合 cas-servlet.xml)：

 

<on-start>
        <evaluate expression="initialFlowSetupAction" />
    </on-start>

<bean id="initialFlowSetupAction" class="org.jasig.cas.web.flow.InitialFlowSetupAction"
        p:argumentExtractors-ref="argumentExtractors"
        p:warnCookieGenerator-ref="warnCookieGenerator"
        p:ticketGrantingTicketCookieGenerator-ref="ticketGrantingTicketCookieGenerator"/>

     3.4 InitialFlowSetupAction

 

protected Event doExecute(final RequestContext context) throws Exception {
        final HttpServletRequest request = WebUtils.getHttpServletRequest(context);
        if (!this.pathPopulated) {
            final String contextPath = context.getExternalContext().getContextPath();
            final String cookiePath = StringUtils.hasText(contextPath) ? contextPath + "/" : "/";
            logger.info("Setting path for cookies to: "
                + cookiePath);
            this.warnCookieGenerator.setCookiePath(cookiePath);
            this.ticketGrantingTicketCookieGenerator.setCookiePath(cookiePath);
            this.pathPopulated = true;
        }

        // 给 FlowScope 的设置 ticketGrantingTicketId, warnCookieValue 参数
        context.getFlowScope().put(
            "ticketGrantingTicketId", this.ticketGrantingTicketCookieGenerator.retrieveCookieValue(request));
        context.getFlowScope().put("warnCookieValue",
            Boolean.valueOf(this.warnCookieGenerator.retrieveCookieValue(request)));

         // 3.4.1 抽取 service 参数
        final Service service = WebUtils.getService(this.argumentExtractors, context);

        if (service != null && logger.isDebugEnabled()) {
            logger.debug("Placing service in FlowScope: " + service.getId());
        }

        // 给 FlowScope 的设置 service 参数
        context.getFlowScope().put("service", service);

        return result("success");
    }

     3.4.1  WebApplicationService.getService

public static WebApplicationService getService(
        final List<ArgumentExtractor> argumentExtractors,
        final HttpServletRequest request) {
        for (final ArgumentExtractor argumentExtractor : argumentExtractors) {

            // 3.4.1.1 通过配置的 argumentExtractor 抽取 service
            final WebApplicationService service = argumentExtractor.extractService(request);

            if (service != null) {
                return service;
            }
        }

        return null;
    }

 

     3.4.1.1  CasArgumentExtractor 代码

public final class CasArgumentExtractor extends AbstractSingleSignOutEnabledArgumentExtractor {

    public final WebApplicationService extractServiceInternal(final HttpServletRequest request) {
        return SimpleWebApplicationServiceImpl.createServiceFrom(request, getHttpClientIfSingleSignOutEnabled());
    }
}

// SimpleWebApplicationServiceImpl
    private static final String CONST_PARAM_SERVICE = "service";
    private static final String CONST_PARAM_TARGET_SERVICE = "targetService";
    private static final String CONST_PARAM_TICKET = "ticket";
    private static final String CONST_PARAM_METHOD = "method";

public static SimpleWebApplicationServiceImpl createServiceFrom(
        final HttpServletRequest request, final HttpClient httpClient) {
        final String targetService = request
            .getParameter(CONST_PARAM_TARGET_SERVICE);
        final String method = request.getParameter(CONST_PARAM_METHOD);
        final String serviceToUse = StringUtils.hasText(targetService)
            ? targetService : request.getParameter(CONST_PARAM_SERVICE);

        if (!StringUtils.hasText(serviceToUse)) {
            return null;
        }

        final String id = cleanupUrl(serviceToUse);
        final String artifactId = request.getParameter(CONST_PARAM_TICKET);

        return new SimpleWebApplicationServiceImpl(id, serviceToUse,
            artifactId, "POST".equals(method) ? ResponseType.POST
                : ResponseType.REDIRECT, httpClient);
    }

private SimpleWebApplicationServiceImpl(final String id,
        final String originalUrl, final String artifactId,
        final ResponseType responseType, final HttpClient httpClient) {
        super(id, originalUrl, artifactId, httpClient);
        this.responseType = responseType;
    }

protected AbstractWebApplicationService(final String id, final String originalUrl, final String artifactId, final HttpClient httpClient) {
        this.id = id;
        this.originalUrl = originalUrl;
        this.artifactId = artifactId;
        this.httpClient = httpClient;
    }

 

 

3. Cas20ProxyReceivingTicketValidationFilter 及 AbstractTicketValidationFilter代码：

Java代码  

public final void doFilter(final ServletRequest servletRequest, final ServletResponse servletResponse, final FilterChain filterChain) throws IOException, ServletException {

        if (!preFilter(servletRequest, servletResponse, filterChain)) {
            return;
        }

        final HttpServletRequest request = (HttpServletRequest) servletRequest;
        final HttpServletResponse response = (HttpServletResponse) servletResponse;
        final String ticket = CommonUtils.safeGetParameter(request, getArtifactParameterName());

        // 如果 URL 中包含 ticket 参数，则执行 service 验证工作
        if (CommonUtils.isNotBlank(ticket)) {
            if (log.isDebugEnabled()) {
                log.debug("Attempting to validate ticket: " + ticket);
            }

            try {

                final Assertion assertion = this.ticketValidator.validate(ticket, constructServiceUrl(request, response));

                if (log.isDebugEnabled()) {
                    log.debug("Successfully authenticated user: " + assertion.getPrincipal().getName());
                }

                request.setAttribute(CONST_CAS_ASSERTION, assertion);

                if (this.useSession) {
                    request.getSession().setAttribute(CONST_CAS_ASSERTION, assertion);
                }
                onSuccessfulValidation(request, response, assertion);

                if (this.redirectAfterValidation) {
                    log. debug("Redirecting after successful ticket validation.");
                    response.sendRedirect(constructServiceUrl(request, response));
                    return;
                }
            } catch (final TicketValidationException e) {
                response.setStatus(HttpServletResponse.SC_FORBIDDEN);
                log.warn(e, e);

                onFailedValidation(request, response);

                if (this.exceptionOnValidationFailure) {
                    throw new ServletException(e);
                }

                return;
            }
        }

        // 如果不包含 ticket， 直接跳过CAS Filter验证，继续其他 filter 或 web app 操作
        filterChain.doFilter(request, response);

    }