public function generateDeviceValidationToken($username)
    {
        $this->username = $username;
        $validationToken = $this->crypt()->generateRandomString(6, '0123456789');

        $devices = $this->getMeta()->allowedDevices;

        $devices[] = [
            'device'          => $this->getDeviceFingerprint(),
            'created'         => 0,
            'token'           => '',
            'validationToken' => $validationToken,
            'confirmed'       => false
        ];

        $this->getMeta()->allowedDevices = $devices;
        $this->getMeta()->save();

        return $validationToken;
    }