wx_getopenid api

<?php
$appid = "************";
$secret = "***********";
if (!isset ( $_GET [‘code‘] )) {
	$back_url = $_GET [‘back_url‘];

	if ($back_url) {
		$back_url_arr = parse_url ( $back_url );
		$arr_allow_url = array (
				‘hk.4vtk.com‘,
				‘open.weixin.qq.com‘
		);
		if (in_array ( $back_url_arr [‘host‘], $arr_allow_url )) {
			Session_start();
			$_SESSION[‘back_url‘]=$back_url;
			$local_url = "http://{$_SERVER [‘HTTP_HOST‘]}{$_SERVER[‘PHP_SELF‘]}";
			$local_url=urlencode($local_url);
			$sit = "https://open.weixin.qq.com/connect/oauth2/authorize?appid={$appid}&redirect_uri={$local_url}&response_type=code&scope=snsapi_base&state=1#wechat_redirect";

			header ( "Location:" . $sit );
		}else{
			echo "<h2>未经授权的url</h2>";
			exit ();
		}

	} else {
		echo "<h2>回调url错误</h2>";
		exit ();
	}

} else {
	$code = $_GET [‘code‘];
	$url = "https://api.weixin.qq.com/sns/oauth2/access_token?appid=" . $appid . "&secret=" . $secret . "&code=" . $code . "&grant_type=authorization_code";
	$json = json_decode ( file_get_contents ( $url ), true );
	Session_start();
	$back_url=$_SESSION[‘back_url‘];
	$arr_back_url=parse_url($back_url);
	if($arr_back_url[‘query‘]){
		$return_url = $back_url . "&openid=" . $json [‘openid‘];
	}else{
		$return_url = $back_url . "?openid=" . $json [‘openid‘];
	}

	header ( "Location:" . $return_url );

}

?>