完整的PHP 微信 退款类操作，详细如下，完整页面下载在底部：

use think\Config;
//微信申请退款类
class Refund{
	protected $config = null;
	private $appid;//公众账号appid
	private $mch_id;//商户号
	private $nonce_str;//随机字符串，不长于32位
	private $sign; //                                                                                 签名
	private $transaction_id;//微信生成的订单号，在支付通知中有返回
	private $out_refund_no;//商户退款单号商户系统内部的退款单号，商户系统内部唯一，只能是数字、大小写字母_-|*@ 
	private $total_fee;//total_fee订单总金额，单位为分，只能为整数
	private $refund_fee;//退款金额
	private $refund_desc='接单员暂时都没有空，麻烦您提价，或稍后再发一次';//退款原因;
	private $api_password;  //商户平台设置的密钥key
	private $refundurl = "https://api.mch.weixin.qq.com/secapi/pay/refund";
	 /** 公钥*/
	private $apiclient_cert;
	/** 私钥*/
	private $apiclient_key;
	/** ca证书*/
 	private $rootca;
	public function __construct(){
		 $this->config = Config::get();
		 //初始化红包设置信息
		 $this->appid = $this->config["wechat"]["app_id"];
		 $this->mch_id = $this->config["wechat"]["payment"]["mch_id"];
		 $this->api_password = $this->config["wechat"]["payment"]["key"];
		 $this->nonce_str = $this->create_nonce_str(32);
		 $this->apiclient_cert  = EXTEND_PATH . 'wxcert' . DS . 'apiclient_cert.pem';
		 $this->apiclient_key = EXTEND_PATH . 'wxcert' . DS . 'apiclient_key.pem';
		 $this->rootca = EXTEND_PATH . 'wxcert' . DS . 'rootca.pem';
		 
		 }
    //发出退款请求
	public function send_post($transaction_id="",$out_refund_no='',$refund_fee=0,$total_fee=0){
		 $sign = $this->create_sign($transaction_id, $out_refund_no, $refund_fee, $total_fee);
		 $send_array = array(
			 'appid'       	=> $this->appid,
			 'mch_id'        => $this->mch_id,
			 'nonce_str'     => $this->nonce_str,
			 'out_refund_no' => $out_refund_no,
			 'refund_desc'   => $this->refund_desc,
			 'refund_fee'    => $refund_fee,
			 'total_fee'     => $total_fee,
			 'transaction_id'=> $transaction_id	,
			 'sign' => $sign,
		 );
		 $send_xml = $this->toxml($send_array);
		 $result = $this->get_curl_contents($this->refundurl, $send_xml);
		 if($result){
		 	$data = $this->xmlToArray($result);
			return $data;
		 }
		 else{
		 	return null;
		 }
		 

	}
	
	//生成随机字符串
		 public function create_nonce_str($length){
		 $str = null;
		 $strPol = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz";
		 $max = strlen($strPol)-1;
		 for($i=0;$i<$length;$i++){
		 	$str.=$strPol[rand(0,$max)];//rand($min,$max)生成介于min和max两个数

之间的一个随机整数
		 }
		 return $str;
		 }

	/**
	 
	    创建签名
		例如：
		appid： wxd111665abv58f4f
		mch_id： 10000100
		device_info： 1000
		Body： test
		nonce_str： ibuaiVcKdpRxkhJA
		第一步：对参数按照 key=value 的格式，并按照参数名 ASCII 字典序排序如下：
		stringA="appid=wxd930ea5d5a258f4f&body=test&device_info=1000&mch_i
		d=10000100&nonce_str=ibuaiVcKdpRxkhJA";
		第二步：拼接支付密钥：
		stringSignTemp="stringA&key=192006250b4c09247ec02edce69f6a2d"
		sign=MD5(stringSignTemp).toUpperCase()="9A0A8659F005D6984697E2CA0A
		9CF3B7"
		*/	
		private function create_sign($transaction_id="",$out_refund_no='',$refund_fee=0,

$total_fee=0){
			$string_array = array(
					'appid'       	=> $this->appid,
					'mch_id'        => $this->mch_id,
					'nonce_str'     => $this->nonce_str,
					'out_refund_no' => $out_refund_no,
					'refund_desc'   => $this->refund_desc,
					'refund_fee'    => $refund_fee,
					'total_fee'     => $total_fee,
					'transaction_id'=> $transaction_id
				);
				$stringA = "";
					foreach($string_array as $key =>$value){
						if(!empty($value)){
						$stringA .= "$key=$value";
						if($key != 'transaction_id'){$stringA .= '&';}
					}
				}
				$stringSignTemp="$stringA&key=$this->api_password";
				$sign = MD5($stringSignTemp);
				$sign = strtoupper($sign);
				return $sign;
		}
		public function toxml($arr){
			  $xml = "<xml>";
			  foreach ($arr as $key=>$val)
			  {
			   $xml.="<".$key."><![CDATA[".$val."]]></".$key.">"; 
			  }
			  $xml.="</xml>";
			  return $xml; 
		
	}

	private function xmlToArray($postStr){
		$msg = array();
		$msg = (array)simplexml_load_string($postStr, 'SimpleXMLElement', LIBXML_NOCDATA);
		return $msg;
	}

	//curl获取请求文本内容
	public function get_curl_contents($url, $data = null) {
			$curl = curl_init(); //初始化
    		curl_setopt($curl, CURLOPT_URL, $url);//设置抓取的url 为 $requesturl
    		curl_setopt($curl, CURLOPT_HEADER, 0);//设置头文件的信息作为数据流输出
    		curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
    		//设置获取的信息以文件流的形式返回，而不是直接输出。
    		curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false); //跳过证书验证
    		curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, false);  // 从证书中检查SSL加密算法是否存在
    		
    		curl_setopt($curl,CURLOPT_SSLCERTTYPE,'PEM');
		    curl_setopt($curl,CURLOPT_SSLCERT,$this->apiclient_cert);    
		    curl_setopt($curl,CURLOPT_SSLKEYTYPE,'PEM');
		    curl_setopt($curl,CURLOPT_SSLKEY,$this->apiclient_key);
		    curl_setopt($curl,CURLOPT_SSLKEYTYPE,'PEM');
		    //echo $this->rootca;
		    curl_setopt($curl,CURLOPT_CAINFO,$this->rootca);
			if (!empty($data)){
		        curl_setopt($curl, CURLOPT_POST, 1);  //POST请求
		        curl_setopt($curl, CURLOPT_POSTFIELDS, $data);
		    } 
    		$data = curl_exec($curl);//执行命令
    		curl_close($curl);//关闭URL请求
		    return $data;
	}

	public function get_server_ip(){
	    if('/'==DIRECTORY_SEPARATOR){
	      $server_ip=$_SERVER['SERVER_ADDR'];
	    }else{
	      $server_ip=@gethostbyname($_SERVER['SERVER_NAME']);
	    }
    		return $server_ip;
	}
}

PHP微信退款类下载