public function getLoginUrl()
    {
        // required params
        $params = array(
            'client_id' => $this->getClientId(),
            'redirect_uri' => $this->getRedirectUri(),
        );
        // optional params
        if ($this->getScope()) {
            $params['scope'] = implode(',', $this->getScope());
        }
        if ($this->getResponceType()) {
            $params['response_type'] = $this->getResponceType();
        }
        if ($this->apiVersion) {
            $params['v'] = $this->apiVersion;
        }
        if ($this->state) {
            $params['state'] = $this->state;
        }

        return 'https://oauth.vk.com/authorize?' . http_build_query($params);
    }