获取微信access_token

/**
 * 获取微信access_token
 * @return mixed
 */
function get_access_token() {
   $appId = C('APPID');
    $secret = C('APPSECRET');
   $access_token = '';
   $url_token = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=".$appId."&secret=".$secret;
   $str_json_access_token = curl_get($url_token);
   if(!empty($str_json_access_token)){
      $array_json_access_token = json_decode($str_json_access_token,true);
      $access_token =  $array_json_access_token['access_token'];
   } 
    return     $access_token;
}