public function authURL($state)
    {
        $url = $this->settings['authentication_url'];

        $params = [
            'client_id' => $this->settings('api_key'),
            'redirect_uri' => $this->settings('redirect_uri'),
            'scope' => $this->settings('permissions'),
            'state' => $state,
        ];

        return $url.'?'.http_build_query($params);
    }