<?php

$otp      = "cccccccvfckdvfblijjfctibtlrbejjddjiligvbkevu";   // OTP from Yubikey
$yubikeyid   = substr($otp, 0, 12);               // Grab first 12 chars for unique userid

$apiserver1 = "https://api.yubico.com/wsapi/verify?id=1&otp=";      // Yubico API server

$serverresponse = file_get_contents($apiserver1 . $otp);      // Access server using concat string of URL plus OTP
$pos = strpos($serverresponse, "status=OK");            // Check the server response for "status=ok"

if ($pos === false) {                     // If the string is not returned there is an error
    echo "$yubikeyid - Invalid<BR><BR> - $serverresponse";
} else {                        // Else the string was found and the Yubikey is valid, now check the userid etc...
    echo "$yubikeyid -  OK<BR><BR> - $serverresponse";
}

?>