cas客户端的端登录问题求解，异常如下

2012-1-11 15:25:54 edu.yale.its.tp.cas.client.CASReceipt getReceipt
严重: edu.yale.its.tp.cas.client.CASAuthenticationException: Unable to validate ProxyTicketValidator [[edu.yale.its.tp.cas.client.ProxyTicketValidator proxyList=[null] [edu.yale.its.tp.cas.client.ServiceTicketValidator casValidateUrl=[https://cas.hundsun.com:8443/cas/serviceValidate] ticket=[ST-73-gicvl1BIeG9b5LdPWBFz-cas] service=[http%3A%2F%2Flocalhost%3A8086%2FCasTest%2Findex.jsp] renew=false]]]
2012-1-11 15:25:54 edu.yale.its.tp.cas.client.filter.CASFilter doFilter
严重: edu.yale.its.tp.cas.client.CASAuthenticationException: Unable to validate ProxyTicketValidator [[edu.yale.its.tp.cas.client.ProxyTicketValidator proxyList=[null] [edu.yale.its.tp.cas.client.ServiceTicketValidator casValidateUrl=[https://cas.hundsun.com:8443/cas/serviceValidate] ticket=[ST-73-gicvl1BIeG9b5LdPWBFz-cas] service=[http%3A%2F%2Flocalhost%3A8086%2FCasTest%2Findex.jsp] renew=false]]]
2012-1-11 15:25:54 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet jsp threw exception
sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:174)
at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:238)
at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:280)

补充：Java ,  Java EE