统一支付接口中，缺少必填参数openid！trade_type为JSAPI时，openid为必填参数！

    $jsApi = new JsApi_pub();
    //=========步骤1：网页授权获取用户openid============
    //通过code获得openid
 if (!isset($_GET['code']))
{
     //触发微信返回code码
     $url = $jsApi->createOauthUrlForCode(WxPayConf_pub::JS_API_CALL_URL);
     Header("Location: $url"); 
}else{
    //获取code码，以获取openid
     $code = $_GET['code'];
    $jsApi->setCode($code);
    $openid = $jsApi->getOpenId();
    echo $openid;   这里获取不到
    echo "
";
 }
    $unifiedOrder = new UnifiedOrder_pub();
    $unifiedOrder->setParameter("openid","$openid");//商品描述
    $unifiedOrder->setParameter("body","微信支付测试");//商品描述

回复内容：

    $jsApi = new JsApi_pub();
    //=========步骤1：网页授权获取用户openid============
    //通过code获得openid
 if (!isset($_GET['code']))
{
     //触发微信返回code码
     $url = $jsApi->createOauthUrlForCode(WxPayConf_pub::JS_API_CALL_URL);
     Header("Location: $url"); 
}else{
    //获取code码，以获取openid
     $code = $_GET['code'];
    $jsApi->setCode($code);
    $openid = $jsApi->getOpenId();
    echo $openid;   这里获取不到
    echo "
";
 }
    $unifiedOrder = new UnifiedOrder_pub();
    $unifiedOrder->setParameter("openid","$openid");//商品描述
    $unifiedOrder->setParameter("body","微信支付测试");//商品描述

BeeCloud对各种支付渠道的API做了封装，提供了一套REST API框架，你可以参考下