<?PHP
    if(isset($_POST['key'])){
        header('Content-type: application/x-x509-user-cert');
        header('Content-disposition: attachment; filename=user.crt');
        include('File/X509.php');

        $capem = '-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----';

        $subject = new File_X509();
        $subject->loadCA($capem);
        $subject->loadSPKAC($_POST['key']);
        $subject->setDN('CN=Username');

        $issuer = new File_X509();
        $issuer->loadX509($capem);
        $cakey = new Crypt_RSA();
        $cakey->loadKey('-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----');
        $issuer->setPrivateKey($cakey);

        $x509 = new File_X509();
        $cert = $x509->sign($issuer, $subject);

        $x509->loadX509($cert);
$x509->setExtension('id-ce-keyUsage', array('digitalSignature', 'keyEncipherment', 'dataEncipherment'));
$x509->setExtension('id-ce-extKeyUsage', array('id-kp-serverAuth', 'id-kp-clientAuth'));
        $x509->setStartDate('-1 day');
        $x509->setEndDate('+ 3 year');
        $x509->setSerialNumber('12356', 10);
        $cert = $x509->sign($issuer, $x509);

        echo $x509->saveX509($cert);
    }else{
?>
<form method="POST">
    <keygen name="key" keytype="RSA" challenge="ucert">
    <button>SEND</button>
</form>
<?PHP
    }
?>