CAS 数据库校验

1. UnknownUsernameAuthenticationException --> BadUsernameOrPasswordAuthenticationException --> BadCredentialsAuthenticationException --> AuthenticationException -->

  Exception

2. AuthenticationManagerImpl类

    调用authenticateAndObtainPrincipal先检查是否支持credentials，

    然后authenticationHandler.authenticate(credentials)，

    然后doAuthentication(credentials) ，

    然后authenticateUsernamePasswordInternal((UsernamePasswordCredentials) credentials)，

    然后QueryDatabaseAuthenticationHandler调用，authenticateUsernamePasswordInternal验证数据库

3. 抛出BadCredentialsAuthenticationException.ERROR异常

     /**
* @throws IllegalArgumentException
* if the ServiceTicketId or the Credentials are null.
*/
@Audit(action = "PROXY_GRANTING_TICKET",
actionResolverName = "GRANT_PROXY_GRANTING_TICKET_RESOLVER",
resourceResolverName = "GRANT_PROXY_GRANTING_TICKET_RESOURCE_RESOLVER")
@Profiled(tag = "GRANT_PROXY_GRANTING_TICKET", logFailuresSeparately = false)
@Transactional(readOnly = false)
public String delegateTicketGrantingTicket(final String serviceTicketId,
final Credentials credentials) throws TicketException
    转化为AuthenticationException e，

    转化为TicketCreationException(e)

4. CaptchaAuthenticationViaFormAction类

     try {
WebUtils.putTicketGrantingTicketInRequestScope(context, this.centralAuthenticationService.createTicketGrantingTicket(credentials));
putWarnCookieIfRequestParameterPresent(context);
return "success";
} catch (final TicketException e) {
populateErrorsInstance(e, messageContext);
return "error";
}     捕获异常，进入populateErrorsInstance(e, messageContext);
      private void populateErrorsInstance(final TicketException e, final MessageContext messageContext) {

try {
messageContext.addMessage(new MessageBuilder().error().code(e.getCode()).defaultText(e.getCode()).build());
} catch (final Exception fe) {
logger.error(fe.getMessage(), fe);
}
}       通过MessageContext，Spring的机制输出到页面<form:form errors/>