让CAS支持客户端自定义登陆页面——服务器篇

这篇讲解如何对CAS服务器端进行修改。

修改需要基于几个基本原则：

1. 不影响原有统一登陆界面功能
2. 客户端应尽量保持简单
3. 尽量保证原有功能的完整性和安全性

对于第三点，必须事先说明：将登陆页面放到客户端本身就是降低了CAS安全性，这意味着作为服务向外发布的CAS服务器中的用户密码有可能由于客户端的不安全性而导致泄露，整个CAS系统成为了一个“水桶形态”，整个CAS体系的安全性将取决于所有客户端中安全性最低的一个。这也是CAS官方一直不推荐的方式。

接下来我们讲解服务器端修改的详细过程：

首先，修改/WEB-INF/web.xml，为cas增加一个/remoteLogin的映射：

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

然后修改cas-servlet.xml文件，增加我们对/remoteLogin映射的处理，需要增加一个新流程：

<bean id="handlerMappingB" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
    <property name="mappings">
        <props>
            <prop key="/login">loginController</prop>
            <prop key="/remoteLogin">remoteLoginController</prop>
        </props>
    </property>
    <property name="interceptors">
        <list>
            <ref bean="localeChangeInterceptor" />
        </list>
    </property>
</bean>

然后在cas-servlet.xml文件中添加我们上面所配置的remoteController的bean：

<!-- 增加远程控制者，允许以/remote请求启动remote控制流程 -->
<bean id="remoteLoginController"
    class="org.springframework.webflow.executor.mvc.FlowController"
    p:flowExecutor-ref="remoteLoginFlowExecutor"
    p:defaultFlowId="remoteLogin-webflow">
    <property name="argumentHandler">
        <bean
class="org.springframework.webflow.executor.support.RequestParameterFlowExecutorArgumentHandler"
            p:flowExecutionKeyArgumentName="lt"
            p:defaultFlowId="remoteLogin-webflow" />
    </property>
</bean>
<flow:executor id="remoteLoginFlowExecutor" registry-ref="remoteLoginFlowRegistry">
    <flow:execution-attributes>
        <flow:alwaysRedirectOnPause value="false"/>
    </flow:execution-attributes>
</flow:executor>
<flow:registry id="remoteLoginFlowRegistry">
    <flow:location path="/WEB-INF/remoteLogin-webflow.xml"/>
</flow:registry>

可以看到上面将请求指向了webflow配置文件/WEB-INF/remoteLogin-webflow.xml文件，我们需要创建此文件并配置其成为我们所需的流程，以下是remoteLogin-webflow.xml全文：

<?xml version="1.0" encoding="UTF-8"?>
<flow xmlns="http://www.springframework.org/schema/webflow"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
              http://www.springframework.org/schema/webflow
              http://www.springframework.org/schema/webflow/spring-webflow-1.0.xsd">
    <start-state idref="remoteLogin"/>
    <!-- 远程登陆主要Action -->
    <action-state id="remoteLogin">
        <action bean="remoteLoginAction" />
        <transition on="error" to="remoteCallbackView" />
        <transition on="submit" to="bindAndValidate" />
        <transition on="checkTicketGrantingTicket" to="ticketGrantingTicketExistsCheck" />
    </action-state>
    <!-- 远程回调页面，主要以JavaScript的方式回传一些参数用 -->
    <end-state id="remoteCallbackView" view="remoteCallbackView" />
   
    <decision-state id="ticketGrantingTicketExistsCheck">
        <if test="${flowScope.ticketGrantingTicketId != null}" then="hasServiceCheck"
else="gatewayRequestCheck" />
    </decision-state>
    <decision-state id="gatewayRequestCheck">
        <if test="${externalContext.requestParameterMap['gateway'] != '' &amp;&amp; externalContext.requestParameterMap['gateway'] != null &amp;&amp; flowScope.service != null}" then="redirect" else="remoteCallbackView" />
    </decision-state>
   
    <decision-state id="hasServiceCheck">
        <if test="${flowScope.service != null}" then="generateServiceTicket" else="remoteCallbackView" />
    </decision-state>
   
    <!--
        The "warn" action makes the determination of whether to redirect directly to the
requested
        service or display the "confirmation" page to go back to the server.
    -->
    <decision-state id="warn">
        <if test="${flowScope.warnCookieValue}" then="showWarningView" else="redirect" />
    </decision-state>
    <action-state id="bindAndValidate">
        <action bean="authenticationViaFormAction" />
        <transition on="success" to="submit" />
        <transition on="error" to="remoteCallbackView" />
    </action-state>
   
    <action-state id="submit">
        <action bean="authenticationViaFormAction" method="submit" />
        <transition on="warn" to="warn" />
        <transition on="success" to="sendTicketGrantingTicket" />
        <transition on="error" to="remoteCallbackView" />
    </action-state>
   
    <action-state id="sendTicketGrantingTicket">
        <action bean="sendTicketGrantingTicketAction" />
        <transition on="success" to="serviceCheck" />
    </action-state>
    <decision-state id="serviceCheck">
        <if test="${flowScope.service != null}" then="generateServiceTicket"
else="remoteCallbackView" />
    </decision-state>
   
    <action-state id="generateServiceTicket">
        <action bean="generateServiceTicketAction" />
        <transition on="success" to ="warn" />
        <transition on="error" to="remoteCallbackView" />
        <transition on="gateway" to="redirect" />
    </action-state>
    <!--
        The "showWarningView" end state is the end state for when the user has requested
privacy settings (to be "warned") to be turned on. It delegates to a
        view defines in default_views.properties that display the "Please click here to go
to the service." message.
    -->
    <end-state id="showWarningView" view="casLoginConfirmView" />
    <!--
        The "redirect" end state allows CAS to properly end the workflow while still
redirecting
        the user back to the service required.
    -->
    <end-state id="redirect" view="bean:dynamicRedirectViewSelector" />
   
    <end-state id="viewServiceErrorView" view="viewServiceErrorView" />
   
    <end-state id="viewServiceSsoErrorView" view="viewServiceSsoErrorView" />
    <global-transitions>
        <transition to="viewServiceErrorView" on-
exception="org.springframework.webflow.execution.repository.NoSuchFlowExecutionException" /
>
        <transition to="viewServiceSsoErrorView" on-
exception="org.jasig.cas.services.UnauthorizedSsoServiceException" />
        <transition to="viewServiceErrorView" on-
exception="org.jasig.cas.services.UnauthorizedServiceException" />
    </global-transitions>
</flow>

以上文件根据原login-webflow.xml文件修改，粗体为修改部分。可以看到，我们在流程中增加了remoteLogin Action节点和remoteCallback View节点，下面我们配置remoteLogin节点：
在/WEB-INF/cas-servlet.xml文件中增加remoteLoginAction配置：

<bean id="remoteLoginAction"
    class="com.baidu.cas.web.flow.RemoteLoginAction"
    p:argumentExtractors-ref="argumentExtractors"
    p:warnCookieGenerator-ref="warnCookieGenerator"
    p:ticketGrantingTicketCookieGenerator-ref="ticketGrantingTicketCookieGenerator" />

同时创建com.baidu.cas.web.flow.RemoteLoginAction类：

/**
* 远程登陆票据提供Action.
* 根据InitialFlowSetupAction修改.
* 由于InitialFlowSetupAction为final类，因此只能将代码复制过来再进行修改.
*
* @author GuoLin
*/
public class RemoteLoginAction extends AbstractAction {
    /** CookieGenerator for the Warnings. */
    @NotNull
    private CookieRetrievingCookieGenerator warnCookieGenerator;
    /** CookieGenerator for the TicketGrantingTickets. */
    @NotNull
    private CookieRetrievingCookieGenerator ticketGrantingTicketCookieGenerator;
    /** Extractors for finding the service. */
    @NotEmpty
    private List<ArgumentExtractor> argumentExtractors;
    /** Boolean to note whether we've set the values on the generators or not. */
    private boolean pathPopulated = false;
    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;
        }
        context.getFlowScope().put("ticketGrantingTicketId",
                this.ticketGrantingTicketCookieGenerator.retrieveCookieValue(request));
        context.getFlowScope().put("warnCookieValue",
                Boolean.valueOf(this.warnCookieGenerator.retrieveCookieValue(request)));
        final Service service = WebUtils.getService(this.argumentExtractors, context);
        if (service != null && logger.isDebugEnabled()) {
            logger.debug("Placing service in FlowScope: " + service.getId());
        }
        context.getFlowScope().put("service", service);
       
        // 客户端必须传递loginUrl参数过来，否则无法确定登陆目标页面
        if (StringUtils.hasText(request.getParameter("loginUrl"))) {
            context.getFlowScope().put("remoteLoginUrl", request.getParameter("loginUrl"));
        } else {
            request.setAttribute("remoteLoginMessage", "loginUrl parameter must be supported.");
            return error();
        }
       
        // 若参数包含submit则进行提交，否则进行验证
        if (StringUtils.hasText(request.getParameter("submit"))) {
            return result("submit");
        } else {
            return result("checkTicketGrantingTicket");
        }
    }
    public void setTicketGrantingTicketCookieGenerator(
        final CookieRetrievingCookieGenerator ticketGrantingTicketCookieGenerator) {
        this.ticketGrantingTicketCookieGenerator = ticketGrantingTicketCookieGenerator;
    }
    public void setWarnCookieGenerator(final CookieRetrievingCookieGenerator warnCookieGenerator) {
        this.warnCookieGenerator = warnCookieGenerator;
    }
    public void setArgumentExtractors(
        final List<ArgumentExtractor> argumentExtractors) {
        this.argumentExtractors = argumentExtractors;
    }
}

以上粗体为修改部分，要求客户端必须传入loginUrl参数，且当客户端传入submit参数时，直接为其提交用户名密码
然后再配置remoteCallbackView显示节点，修改src/default_views.properties文件，增加remoteCallbackView配置：

### 配置远程回调页面
remoteCallbackView.(class)=org.springframework.web.servlet.view.JstlView
remoteCallbackView.url=/WEB-INF/view/jsp/default/ui/remoteCallbackView.jsp

创建/WEB-INF/view/jsp/default/ui/remoteCallbackView.jsp文件：

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%>
<html>
<head>
    <script type="text/javascript">
        var remoteUrl = "${remoteLoginUrl}?validated=true";
        // 构造错误消息
        var errorMessage = "";
        <spring:hasBindErrors name="credentials">
        errorMessage = "&errorMessage=" + encodeURIComponent('<c:forEach
var="error" items="${errors.allErrors}"><spring:message code="${error.code}"
text="${error.defaultMessage}" /></c:forEach>');
        </spring:hasBindErrors>
       
        // 构造service
        var service = "";
        <c:if test="${service != null && service != ''}">
        service = "&service=" + encodeURIComponent("${service}");
        </c:if>
        // 跳转回去
        window.location.href = remoteUrl + errorMessage + service;
    </script>
</head>
<body>
    ${remoteLoginMessage}
</body>
</html>

以上文件注意粗体部分validated=true，这里我们与客户端约定，当客户端登陆页面后带有参数validated=true时，不进行票据认证请求。这是因为，客户端登陆页面为http://clienthost/login.jsp，那么当用户访问URL http://clienthost/login.jsp时，客户端会重定向到CAS中央服务器请求TGT认证，但认证失败后CAS中央认证服务器会重定向到客户端登陆页面并显示登陆框，此时客户端必须以某种规则避免重新请求中央认证服务器认证， 在这里我们与客户端约定，当回发的请求为登陆页面且带有参数validated=true时即不转发TGT认证请求，即 http://
clienthost/login.jsp?validated=true 请求客户端不会重新发送TGT认证请求给中央认证服务器