解决 PayPal IPN 验证中的 "Access Denied" 问题

    $raw_post_array = file_get_contents('php://input');
    $raw_post_array = explode('&', $raw_post_array);

    $myPost = array();
    foreach ($raw_post_array as $keyval) {
      $keyval = explode ('=', $keyval);
      if (count($keyval) == 2)
        $myPost[$keyval[0]] = urldecode($keyval[1]);
    }
    // read the IPN message sent from PayPal and prepend 'cmd=_notify-validate'
    $req = 'cmd=_notify-validate';
    if (function_exists('get_magic_quotes_gpc')) {
      $get_magic_quotes_exists = true;
    }
    foreach ($myPost as $key => $value) {
      if ($get_magic_quotes_exists == true && get_magic_quotes_gpc() == 1) {
        $value = urlencode(stripslashes($value));
      } else {
        $value = urlencode($value);
      }
      $req .= "&$key=$value";
    }

    // Step 2: POST IPN data back to PayPal to validate
    //Operacion: https://ipnpb.paypal.com/cgi-bin/webscr
    //Sandbox: https://ipnpb.sandbox.paypal.com/cgi-bin/webscr
    $ch = curl_init('https://ipnpb.sandbox.paypal.com/cgi-bin/webscr');
    curl_setopt($ch, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1);
    curl_setopt($ch, CURLOPT_POST, 1);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $req);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 1);
    curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2);
    curl_setopt($ch, CURLOPT_FORBID_REUSE, 1);
    // 修改 CURLOPT_HTTPHEADER 添加 User-Agent
    curl_setopt($ch, CURLOPT_HTTPHEADER, array('Connection: Close', 'User-Agent: YourCompanyName'));
    // In wamp-like environments that do not come bundled with root authority certificates,
    // please download 'cacert.pem' from "https://curl.haxx.se/docs/caextract.html" and set
    // the directory path of the certificate as shown below:
    // curl_setopt($ch, CURLOPT_CAINFO, dirname(__FILE__) . '/cacert.pem');
    if ( !($res = curl_exec($ch)) ) {
      // error_log("Got " . curl_error($ch) . " when processing IPN data");
      curl_close($ch);
      exit;
    }
    curl_close($ch);

    // inspect IPN validation result and act accordingly
    if (strcmp ($res, "VERIFIED") == 0) {
      // The IPN is verified, process it:
      // check whether the payment_status is Completed
      // check that txn_id has not been previously processed
      // check that receiver_email is your Primary PayPal email
      // check that payment_amount/payment_currency are correct
      // process the notification
      // assign posted variables to local variables
      $item_name = $_POST['item_name'];
      $item_number = $_POST['item_number'];
      $payment_status = $_POST['payment_status'];
      $payment_amount = $_POST['mc_gross'];
      $payment_currency = $_POST['mc_currency'];
      $txn_id = $_POST['txn_id'];
      $receiver_email = $_POST['receiver_email'];
      $payer_email = $_POST['payer_email'];

      $header = "From: <a class=\"__cf_email__\" data-cfemail=\"137a7d757c537e7c7d76616a3d707c7e\" href=\"/cdn-cgi/l/email-protection\">[email&#160;protected]</a>\nReply-To:".$payer_email."\n";
      $mensaje = "Se recibio " . $item_name . ", status fue: " . $payment_status . ", el recibidor fue: " . $receiver_email . ", el pagador fue: " . $payer_email . ". Se cobro $" . $payment_amount;
      mail('<a class="__cf_email__" data-cfemail="e18c8e8f849398d3d1a1868c80888dcf828e8c" href="/cdn-cgi/l/email-protection\">[email&#160;protected]</a>',$item_name, $mensaje, $header);
      // IPN message values depend upon the type of notification sent.
      // To loop through the &_POST array and print the NV pairs to the screen:
      foreach($_POST as $key => $value) {
        echo $key . " = " . $value . "<br>";
      }
    } else{
      // IPN invalid, log for manual investigation
        $payer = '<a class="__cf_email__" data-cfemail="e78a888982959ed5d7a7808a868e8bc984888a" href="/cdn-cgi/l/email-protection\">[email&#160;protected]</a>';
        $item_name = 'Ha fallado';
      echo "The response from IPN was: <b>" .$res ."</b>";
      $header = "From: <a class=\"__cf_email__\" data-cfemail=\"e0898e868fa08d8f8e859299ce838f8d\" href=\"/cdn-cgi/l/email-protection\">[email&#160;protected]</a>\nReply-To:".$payer."\n";
      $mensaje = "Fue invalido, recibiste " . $res;
      mail('<a class="__cf_email__" data-cfemail="cba6a4a5aeb9b2f9fb8baca6aaa2a7e5a8a4a6" href="/cdn-cgi/l/email-protection\">[email&#160;protected]</a>',$item_name, $mensaje, $header);
    }

curl_setopt($ch, CURLOPT_HTTPHEADER, array('Connection: Close', 'User-Agent: YourCompanyName'));