自定义cas客户端核心过滤器AuthenticationFilter

        关于cas客户端的基本配置这里就不多说了，不清楚的可以参考上一篇博文：配置简单cas客户端。这里是关于cas客户端实现动态配置认证需要开发说明。

         往往业务系统中有些模块或功能是可以不需要登录就可以访问的，但是添加了cas客户端之后，通过cas客户端filter中的url-pattern来设置需要过滤的url，有时根本无法满足实际业务的需求，这里笔者就通过对cas客户端中源码的阅读，和对认证流程的理解，对cas客户端做了些改动，来实现动态配置cas客户端认证范围。

         下面是cas认证的核心配置，其中AuthenticationFilter过滤器为cas客户端核心过滤，下面的url-pattern是配置需要过滤的url，如果我们能编写该过滤器，我们就可以实现动态配置cas客户端的过滤url了。

<!-- cas统一认证  -->
 <filter>
    <filter-name>CASFilter</filter-name>
    <filter-class>org.jasig.cas.client.authentication.AuthenticationFilter</filter-class>
    <init-param>
        <param-name>casServerLoginUrl</param-name>
        <param-value>http://localhost:8080/casServer3/login</param-value>
    </init-param>
    <init-param>
        <param-name>serverName</param-name>
        <param-value>http://localhost:8080</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>CASFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <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>http://localhost:8080/casServer3</param-value>
    </init-param>
    <init-param>
        <param-name>serverName</param-name>
        <param-value>http://localhost:8080</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>CAS Validation Filter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

思路：将配置中指向的核心过滤器，指向自己定义的过滤器，将源码中核心过滤器AuthenticationFilter的代码复制拷贝到该自定义过滤器中，然后在该过滤器中添加自己的过滤规则。

步骤：

1.配置并启动cas服务端，具体配置可以参考博文：搭建简单的cas认证服务

2.新建一个web项目，然后添加cas客户端配置，具体配置可以参考博文：配置简单cas客户端

3.导入cas客户端核心jar的源码到该web项目中，源码在cas客户端下载zip包中就有，一般为cas-client-core文件夹

4.在项目的src中新建类AuthenticationFilter，继承org.jasig.cas.client.util.AbstractCasFilter，打开web.xml文件，找到找到cas核心过滤器的配置项CASFilter，Ctrl+左键，点击进入org.jasig.cas.client.authentication.AuthenticationFilter类中，复制类里面的全部代码到自定义的AuthenticationFilter类中。修改web.xml中cas核心过滤器配置项CASFilter中的配置，将filter-class指向刚才自定义的AuthenticationFilter类，同时在该过滤器中添加<init-param>配置。如下

<filter>
    <filter-name>CASFilter</filter-name>
    <filter-class>com.supre.filter.AuthenticationFilter</filter-class>
    <init-param>
        <param-name>casServerLoginUrl</param-name>
        <param-value>http://localhost:8080/casServer3/login</param-value>
    </init-param>
    <init-param>
        <param-name>serverName</param-name>
        <param-value>http://localhost:8080</param-value>
    </init-param>
    <init-param>
        <param-name>excludePaths</param-name>
        <param-value>.*[/,\]rest[/,\].*</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>CASFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

说明：

1其中param-name为参数名，这个在过滤器初始化中需要根据该名字来取param-value中的值

2其中param-value的值可以根据需要在filter中制定自己的规则，笔者这里是正则表达式

5.在自定义的AuthenticationFilter中添加自己的代码，来实现认证范围的控制，代码如下：

package com.supre.filter;

import java.io.IOException;

import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.jasig.cas.client.authentication.DefaultGatewayResolverImpl;
import org.jasig.cas.client.authentication.GatewayResolver;
import org.jasig.cas.client.util.AbstractCasFilter;
import org.jasig.cas.client.util.CommonUtils;
import org.jasig.cas.client.validation.Assertion;
/**
 * 为了方便控制filter，自定义了统一认证过滤器AuthenticationFilter
 * @author Administrator
 *
 */
public class AuthenticationFilter extends AbstractCasFilter{
     /**
     * The URL to the CAS Server login.
     */
    private String casServerLoginUrl;

    /**
     * Whether to send the renew request or not.
     */
    private boolean renew = false;

    /**
     * Whether to send the gateway request or not.
     */
    private boolean gateway = false;
    /**
     * 添加属性，这里用来存放不过滤地址正则表达式，可以根据自己需求定制---1
     */
    private String excludePaths;

    private GatewayResolver gatewayStorage = new DefaultGatewayResolverImpl();

    protected void initInternal(final FilterConfig filterConfig) throws ServletException {
        if (!isIgnoreInitConfiguration()) {
            super.initInternal(filterConfig);
            setCasServerLoginUrl(getPropertyFromInitParams(filterConfig, "casServerLoginUrl", null));
            log.trace("Loaded CasServerLoginUrl parameter: " + this.casServerLoginUrl);
            setRenew(parseBoolean(getPropertyFromInitParams(filterConfig, "renew", "false")));
            log.trace("Loaded renew parameter: " + this.renew);
            setGateway(parseBoolean(getPropertyFromInitParams(filterConfig, "gateway", "false")));
            log.trace("Loaded gateway parameter: " + this.gateway);

            final String gatewayStorageClass = getPropertyFromInitParams(filterConfig, "gatewayStorageClass", null);

            if (gatewayStorageClass != null) {
                try {
                    this.gatewayStorage = (GatewayResolver) Class.forName(gatewayStorageClass).newInstance();
                } catch (final Exception e) {
                    log.error(e,e);
                    throw new ServletException(e);
                }
            }
            //自定义添加代码，用来读取web配置文件中excludes属性值 ---2
            excludePaths = getPropertyFromInitParams(filterConfig, "excludePaths", null);//filterConfig.getInitParameter("excludePaths");
            excludePaths = excludePaths.trim();
        }
    }

    public void init() {
        super.init();
        CommonUtils.assertNotNull(this.casServerLoginUrl, "casServerLoginUrl cannot be null.");
    }
// url判断逻辑，这里大家可以根据自己需要来制订规则
    private boolean isExclude(String uri){
        boolean isInWhiteList = false;
        if(excludePaths!=null&& uri!=null){
            isInWhiteList = uri.matches(excludePaths);
        }
        return isInWhiteList;
    }


    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;
       // 该判断是自定义的对符合条件的url进行通过处理 ---3
        if(isExclude(request.getRequestURI())){
            filterChain.doFilter(request, response);
            return;
        }

        if (assertion != null) {
            filterChain.doFilter(request, response);
            return;
        }

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

        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);
        }

        final String urlToRedirectTo = CommonUtils.constructRedirectUrl(this.casServerLoginUrl, getServiceParameterName(), modifiedServiceUrl, this.renew, this.gateway);

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

        response.sendRedirect(urlToRedirectTo);
    }

    public final void setRenew(final boolean renew) {
        this.renew = renew;
    }

    public final void setGateway(final boolean gateway) {
        this.gateway = gateway;
    }

    public final void setCasServerLoginUrl(final String casServerLoginUrl) {
        this.casServerLoginUrl = casServerLoginUrl;
    }

    public final void setGatewayStorage(final GatewayResolver gatewayStorage) {
        this.gatewayStorage = gatewayStorage;
    }

}

说明：上面的例子笔者是想在web中配置不需要认证的url，通过正则表达式来判断，这里相关的规则可以根据自己需要来编写。

6.到这里就基本完成了，根据自己定义的规则来做测试，大家可以在项目中创建多个jsp或html文件，放在不同目录下(部分设计为通过，部分设计为不通过)，然后在浏览器中直接访问这些文件，看是否被拦截而跳到认证见面，通过根据自己定义的规则判断修改是否成功。