KernelSession::start

public function start(): bool
{
	if ($this->isStarted())
	{
		return true;
	}

	$this->started = true;
	$this->sessionHandler = new CookieSessionHandler($this->lifetime);
	$data = $this->getSessionHandler()->read(self::COOKIE_NAME);
	$this->hash = $this->hashData($data);
	$this->sessionData = unserialize($data, ['allowed_classes' => false]) ?: [];
	if (!isset($this->sessionData['_id']))
	{
		$this->sessionData['_id'] = Random::getString(32, true);
	}
	$this->id = $this->sessionData['_id'];

	return true;
}