扩展acegi以支持验证码

主要是通用改写扩展 AuthenticationProcessingFilter 类加入验证码的校验来实现，当然还有开源框架 JCaptcha 来生成验证码，验证码的生成过程可以去查阅相关的资料，这里只展示后端在验证时的扩展点，代码如下：

public class AuthenticationProcessingFilter implements Filter, InitializingBean, ApplicationEventPublisherAware {
    
    // 省略非关键点代码

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException {
        // ...
        if (requiresAuthentication(httpRequest, httpResponse)) {
            Authentication authResult;
            try {
				//加入验证码
                if(!onPreAuthentication(httpRequest, httpResponse)){
                    httpRequest.getSession().setAttribute(ACEGI_SECURITY_LAST_USERNAME_KEY,
                            username);
                    throw new AuthenticationCodeException("请输入正确的验证码！");
                }
                // 省略非关键代码
        }

        filterChain.doFilter(request, response);
    }

    //加入验证码 
    protected boolean onPreAuthentication(HttpServletRequest request, HttpServletResponse response)
            throws AuthenticationException, IOException {
        String randNum=request.getParameter("randNum");
        String rand=(String)request.getSession().getAttribute("rand");
        if(rand.equals(randNum)){
            return true;
        }
        return false;
    }
    // 省略非关键代码
}