code: @Override
      public NutMap postPay(String url, String key, Map<String, Object> params, File file, String password) {
          params.remove("sign");
          String sign = WxPaySign.createSign(key, params);
          params.put("sign", sign);
          Request req = Request.create(url, METHOD.POST);
          req.setData(Xmls.mapToXml(params));
          Sender sender = Sender.create(req);
          SSLSocketFactory sslSocketFactory;
          try {
              sslSocketFactory = WxPaySSL.buildSSL(file, password);
          }
          catch (Exception e) {
              throw Lang.wrapThrow(e);
          }
          sender.setSSLSocketFactory(sslSocketFactory);
          Response resp = sender.send();
          if (!resp.isOK())
              throw new IllegalStateException("postPay with SSL, resp code=" + resp.getStatus());
          return Xmls.xmlToMap(resp.getContent("UTF-8"));
      }
docs: 微信支付公共POST方法（带证书）
  
  @param url
  请求路径
  @param key
  商户KEY
  @param params
  参数
  @param file
  证书文件
  @param password
  证书密码
  @return