Implementing Google Authenticator 2FA in PHP (ThinkPHP 6)

This article introduces how to download, configure, and use the GoogleAuthenticator PHP class for two‑factor authentication in a ThinkPHP 6 (TP6) environment.

1. Download GoogleAuthenticator class

(1) The code has been tested and works. (2) The code is generated for TP6; adjust the path according to your TP version.

<code>/**
 * PHP Class for handling Google Authenticator 2-factor authentication.
 *
 * @author Michael Kliewe
 * @copyright 2012 Michael Kliewe
 * @license http://www.opensource.org/licenses/bsd-license.php BSD License
 * @link http://www.phpgangsta.de/
 */
class GoogleAuthenticator {
    protected $_codeLength = 6;

    /**
     * Create new secret.
     * 16 characters, randomly chosen from the allowed base32 characters.
     * @param int $secretLength
     * @return string
     */
    public function createSecret($secretLength = 16) {
        $validChars = $this->_getBase32LookupTable();
        if ($secretLength < 16 || $secretLength > 128) {
            throw new Exception('Bad secret length');
        }
        $secret = '';
        $rnd = false;
        if (function_exists('random_bytes')) {
            $rnd = random_bytes($secretLength);
        } elseif (function_exists('mcrypt_create_iv')) {
            $rnd = mcrypt_create_iv($secretLength, MCRYPT_DEV_URANDOM);
        } elseif (function_exists('openssl_random_pseudo_bytes')) {
            $rnd = openssl_random_pseudo_bytes($secretLength, $cryptoStrong);
            if (!$cryptoStrong) {
                $rnd = false;
            }
        }
        if ($rnd !== false) {
            for ($i = 0; $i < $secretLength; ++$i) {
                $secret .= $validChars[ord($rnd[$i]) & 31];
            }
        } else {
            throw new Exception('No source of secure random');
        }
        return $secret;
    }

    /**
     * Calculate the code, with given secret and point in time.
     * @param string $secret
     * @param int|null $timeSlice
     * @return string
     */
    public function getCode($secret, $timeSlice = null) {
        if ($timeSlice === null) {
            $timeSlice = floor(time() / 30);
        }
        $secretkey = $this->_base32Decode($secret);
        $time = chr(0).chr(0).chr(0).chr(0).pack('N*', $timeSlice);
        $hm = hash_hmac('SHA1', $time, $secretkey, true);
        $offset = ord(substr($hm, -1)) & 0x0F;
        $hashpart = substr($hm, $offset, 4);
        $value = unpack('N', $hashpart);
        $value = $value[1] & 0x7FFFFFFF;
        $modulo = pow(10, $this->_codeLength);
        return str_pad($value % $modulo, $this->_codeLength, '0', STR_PAD_LEFT);
    }

    /**
     * Get QR-Code URL for image, from google charts.
     * @param string $name
     * @param string $secret
     * @param string|null $title
     * @param array $params
     * @return string
     */
    public function getQRCodeGoogleUrl($name, $secret, $title = null, $params = array()) {
        $width = !empty($params['width']) && (int)$params['width'] > 0 ? (int)$params['width'] : 200;
        $height = !empty($params['height']) && (int)$params['height'] > 0 ? (int)$params['height'] : 200;
        $level = !empty($params['level']) && array_search($params['level'], array('L','M','Q','H')) !== false ? $params['level'] : 'M';
        $urlencoded = urlencode('otpauth://totp/'.$name.'?secret='.$secret.'');
        if (isset($title)) {
            $urlencoded .= urlencode('&issuer='.urlencode($title));
        }
        return "https://api.qrserver.com/v1/create-qr-code/?data=$urlencoded&size=${width}x${height}&ecc=$level";
    }

    /**
     * Check if the code is correct. This will accept codes starting from $discrepancy*30sec ago to $discrepancy*30sec from now.
     * @param string $secret
     * @param string $code
     * @param int $discrepancy This is the allowed time drift in 30 second units (8 means 4 minutes before or after)
     * @param int|null $currentTimeSlice time slice if we want use other that time()
     * @return bool
     */
    public function verifyCode($secret, $code, $discrepancy = 1, $currentTimeSlice = null) {
        if ($currentTimeSlice === null) {
            $currentTimeSlice = floor(time() / 30);
        }
        if (strlen($code) != 6) {
            return false;
        }
        for ($i = -$discrepancy; $i <= $discrepancy; ++$i) {
            $calculatedCode = $this->getCode($secret, $currentTimeSlice + $i);
            if ($this->timingSafeEquals($calculatedCode, $code)) {
                return true;
            }
        }
        return false;
    }

    /**
     * Set the code length, should be >=6.
     * @param int $length
     * @return GoogleAuthenticator
     */
    public function setCodeLength($length) {
        $this->_codeLength = $length;
        return $this;
    }

    /**
     * Helper class to decode base32.
     * @param string $secret
     * @return bool|string
     */
    protected function _base32Decode($secret) {
        if (empty($secret)) {
            return '';
        }
        $base32chars = $this->_getBase32LookupTable();
        $base32charsFlipped = array_flip($base32chars);
        $paddingCharCount = substr_count($secret, $base32chars[32]);
        $allowedValues = array(6,4,3,1,0);
        if (!in_array($paddingCharCount, $allowedValues)) {
            return false;
        }
        for ($i = 0; $i < 4; ++$i) {
            if ($paddingCharCount == $allowedValues[$i] && substr($secret, -($allowedValues[$i])) != str_repeat($base32chars[32], $allowedValues[$i])) {
                return false;
            }
        }
        $secret = str_replace('=', '', $secret);
        $secret = str_split($secret);
        $binaryString = '';
        for ($i = 0; $i < count($secret); $i = $i + 8) {
            $x = '';
            if (!in_array($secret[$i], $base32chars)) {
                return false;
            }
            for ($j = 0; $j < 8; ++$j) {
                $x .= str_pad(base_convert(@$base32charsFlipped[@$secret[$i + $j]], 10, 2), 5, '0', STR_PAD_LEFT);
            }
            $eightBits = str_split($x, 8);
            for ($z = 0; $z < count($eightBits); ++$z) {
                $binaryString .= (($y = chr(base_convert($eightBits[$z], 2, 10))) || ord($y) == 48) ? $y : '';
            }
        }
        return $binaryString;
    }

    /**
     * Get array with all 32 characters for decoding from/encoding to base32.
     * @return array
     */
    protected function _getBase32LookupTable() {
        return array(
            'A','B','C','D','E','F','G','H',
            'I','J','K','L','M','N','O','P',
            'Q','R','S','T','U','V','W','X',
            'Y','Z','2','3','4','5','6','7',
            '=',
        );
    }

    /**
     * A timing safe equals comparison more info here: http://blog.ircmaxell.com/2014/11/its-all-about-time.html.
     * @param string $safeString The internal (safe) value to be checked
     * @param string $userString The user submitted (unsafe) value
     * @return bool True if the two strings are identical
     */
    private function timingSafeEquals($safeString, $userString) {
        if (function_exists('hash_equals')) {
            return hash_equals($safeString, $userString);
        }
        $safeLen = strlen($safeString);
        $userLen = strlen($userString);
        if ($userLen != $safeLen) {
            return false;
        }
        $result = 0;
        for ($i = 0; $i < $userLen; ++$i) {
            $result |= (ord($safeString[$i]) ^ ord($userString[$i]));
        }
        return $result === 0;
    }
}
</code>

2. Usage

(1) Generate Google secret and QR code. (2) Store the secret and QR code URL in the database.

<code>// Google Authenticator example
$google = new GoogleAuthenticator();
// generate secret
$secret = $google->createSecret();
// generate QR code URL (username is the bound user name)
$qrCodeUrl = $google->getQRCodeGoogleUrl($username, $secret);
// store in database (code omitted)
</code>

3. Verification

<code>$google = new GoogleAuthenticator();
// $google_secret is the stored secret, $code is the user‑provided token
$checkResult = $google->verifyCode($google_secret, $code, 4);
if (!$checkResult) {
    $this->error('Google verification code error');
}
</code>

The above steps demonstrate the complete workflow of integrating Google Authenticator two‑factor authentication into a PHP application.