Facebook 如何测试用户是否是我页面的粉丝

我如何在不请求任何额外权限的情况下测试用户是否是我的facebook页面的粉丝，就像您在[删除不相关facebook垃圾邮件应用程序的链接]上看到的那样。

Php示例：

<?php

$signedRequestObject = parse_signed_request( $_POST["signed_request"],YOUR_APPLICATION_SECRET );

if ($signedRequestObject["page"]){
    // this means this signed_request was generated on a page
    if ($signedRequestObject["page"]["liked"]){
        // the page was liked
    }
}


//used functions
function parse_signed_request($signed_request, $secret) {
  list($encoded_sig, $payload) = explode('.', $signed_request, 2); 
  $sig = $this->base64_url_decode($encoded_sig);
  $data = json_decode($this->base64_url_decode($payload), true);
  if (strtoupper($data['algorithm']) !== 'HMAC-SHA256') {
    echo  'Unknown algorithm. Expected HMAC-SHA256 : ';
    return false;
  }
  $expected_sig = hash_hmac('sha256', $payload, $secret, $raw = true);
  if ($sig !== $expected_sig) {
    echo = 'Bad Signed JSON signature!';
    return false;
  }
  return $data;
}

function base64_url_decode($input) {
  return base64_decode(strtr($input, '-_', '+/'));
}

?>

致命错误：在第17行的D:\Hosting\7564746\html\facebook\b\fan.php中不在对象上下文中时使用$this删除$this引用。。。所以$this->base64\u url\u decode（$encoded\u sig）；变成base64\u url\u decode（$encoded\u sig）；请指定您正在使用的编程语言。