过滤器ActionContext如何获取post传过来的参数

public class CheckAuthFilter implements ActionFilter {

private static final String CHECK_AUTH = ResourceHelper.get("account.check_auth");
private static final String SERVER_WEB_DOMAIN = ResourceHelper.get("server.web.domain");

private static final List<String> excludeURI = new ArrayList<String>(){
    private static final long serialVersionUID = 1L;
    {
        add("/login");
        add("/authorize");
    }};

@Override
public View match(ActionContext ctx) {
    try {
        Object access_token = ctx.getRequest().getSession().getAttribute("access_token");
        Object open_id = ctx.getRequest().getSession().getAttribute("open_id");

       //todo 如何获取post传递过来的参数呢，求大神赐教。
            return null;
        }