原文链接地址： http://lsz1023-126-com.iteye.com/blog/2098973
实现原理：
一、 逻辑
客户端修改CAS Authentication Filter过滤器，该过滤器会判断用户是否登录，如果没有登录则跳转到自身配置的登录界面；
用户输入正确的信息，登录时，会被提交到服务端的登录流程中；
服务端通过新增一个remoteLogin处理类，专门处理客户端自定义登录业务；
该remoteLogin处理类与原始的login处理极为类似，只是修改了获取用户名与密码的方式；
如果用户名与密码不匹配，校验失败，会通过remoteCallbackView.jsp界面将错误提示与service一并响应给客户端的登录界面，接收之后将错误提示显示到界面上；
如果用户名与密码匹配，校验成功，会直接重定向到客户端的service页面，这时CAS Authentication Filter过滤器与CAS Validation Filter过滤器分别校验用户是否登录与ticket票据是否正确，完成最后的校验，否则要求用户重新登录。
二、 修改点
客户端
1. 修改web.xml，修改原先的CAS Authentication Filter过滤器
2. 新增RemoteAuthenticationFilter过滤器
3. 新增login.jsp
服务端
1. 修改web.xml，给cas过滤器添加remoteLogin servlet-mapping映射
2. 新增RemoteLoginAction登录处理类与AuthenticationViaFormAction表单处理类
3. 新增remoteLogin-webflow.xml自定义登录webflow流程文件
4. 修改cas-servlet.xml配置文件，新增一些bean配置
5. 新增remoteCallbackView.jsp响应界面，校验错误时用来通知客户端登录界面。
客户端篇：
1.替换原来过滤器org.jasig.cas.client.authentication.AuthenticationFilter，改成自己的过滤器RemoteAuthenticationFilter.java，这个过滤器可以自己随便放到哪个包中，保证web.xml能够正确引用到就行：
public class RemoteAuthenticationFilter extends AbstractCasFilter
{
public static final String CONST_CAS_GATEWAY = "_const_cas_gateway_";
/**
* 本地登陆页面URL.
*/
private String localLoginUrl;
/**
* 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;
protected void initInternal(final FilterConfig filterConfig)
throws ServletException
{
super.initInternal(filterConfig);
setCasServerLoginUrl(getPropertyFromInitParams(filterConfig,
"casServerLoginUrl", null));
log.trace("Loaded CasServerLoginUrl parameter: "
+ this.casServerLoginUrl);
setLocalLoginUrl(getPropertyFromInitParams(filterConfig,
"localLoginUrl", null));
log.trace("Loaded LocalLoginUrl parameter: " + this.localLoginUrl);
setRenew(Boolean.parseBoolean(getPropertyFromInitParams(filterConfig,
"renew", "false")));
log.trace("Loaded renew parameter: " + this.renew);
setGateway(Boolean.parseBoolean(getPropertyFromInitParams(filterConfig,
"gateway", "false")));
log.trace("Loaded gateway parameter: " + this.gateway);
}
public void init()
{
super.init();
CommonUtils.assertNotNull(this.localLoginUrl,
"localLoginUrl cannot be null.");
CommonUtils.assertNotNull(this.casServerLoginUrl,
"casServerLoginUrl cannot be null.");
}
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 String ticket = request.getParameter(getArtifactParameterName());
final Assertion assertion = session != null ? (Assertion) session
.getAttribute(CONST_CAS_ASSERTION) : null;
final boolean wasGatewayed = session != null
&& session.getAttribute(CONST_CAS_GATEWAY) != null;
// 如果访问路径为localLoginUrl且带有validated参数则跳过
URL url = new URL(localLoginUrl);
final boolean isValidatedLocalLoginUrl = request.getRequestURI()
.endsWith(url.getPath())
&& CommonUtils.isNotBlank(request.getParameter("validated"));
if (!isValidatedLocalLoginUrl && CommonUtils.isBlank(ticket)
&& assertion == null && !wasGatewayed)
{
log.debug("no ticket and no assertion found");
if (this.gateway)
{
log.debug("setting gateway attribute in session");
request.getSession(true).setAttribute(CONST_CAS_GATEWAY, "yes");
}
final String serviceUrl = constructServiceUrl(request, response);
if (log.isDebugEnabled())
{
log.debug("Constructed service url: " + serviceUrl);
}
String urlToRedirectTo = CommonUtils.constructRedirectUrl(
this.casServerLoginUrl, getServiceParameterName(),
serviceUrl, this.renew, this.gateway);
// 加入localLoginUrl
urlToRedirectTo += (urlToRedirectTo.contains("?") ? "&" : "?")
+ "loginUrl=" + URLEncoder.encode(localLoginUrl, "utf-8");
if (log.isDebugEnabled())
{
log.debug("redirecting to \"" + urlToRedirectTo + "\"");
}
response.sendRedirect(urlToRedirectTo);
return;
}
if (session != null)
{
log.debug("removing gateway attribute from session");
session.setAttribute(CONST_CAS_GATEWAY, null);
}
filterChain.doFilter(request, response);
}
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 setLocalLoginUrl(String localLoginUrl)
{
this.localLoginUrl = localLoginUrl;
}
}
2.web.xml中配置：
旧配置
CAS Authentication Filter org.jasig.cas.client.authentication.AuthenticationFilter casServerLoginUrl https://localhost:8443/cas/login serverName http://localhost:8080 renew false gateway false
修改成这样，注：其它路径mapping不用改。
CAS Authentication Filter org.demo.user.common.RemoteAuthenticationFilter localLoginUrl http://localhost:8080/app/mylogin.jsp casServerLoginUrl https://localhost:8443/cas/remoteLogin serverName http://localhost:8080
3.加上你自己定义的登录界面，注：我修改了一些网上介绍的代码：
<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%>APP1客户端登录 APP1客户端登录