public static function getAuthorizationLink(
        $client_id,
        $redirect_url,
        $state = '',
        $url = 'https://runkeeper.com/apps/authorize'
    ) {
        $data = array(
            'client_id' => $client_id,
            'response_type' => 'code',
            'redirect_uri' => $redirect_url,
            'state' => $state,
        );
        return (string) \Guzzle\Http\Url::factory($url)->setQuery($data);
    }