CAS CLIENT客户端配置
弄了两天，终于把CAS CLIENT配置好了，主要是一个小问题，FILTER加载顺序有关系，正确配置如下：
The correct order of the filters in web.xml is necessary:
1. AuthenticationFilter
2. TicketValidationFilter (whichever one is chosen)
3. HttpServletRequestWrapperFilter
4. AssertionThreadLocalFilter
