For getting user access key use following command:

$oauth = new VK\OAuth\VKOAuth();
$client_id = 1234567;
$redirect_uri = 'https://example.com/vk';
$display = VK\OAuth\VKOAuthDisplay::PAGE;
$scope = [VK\OAuth\Scopes\VKOAuthUserScope::WALL, VK\OAuth\Scopes\VKOAuthUserScope::GROUPS];
$state = 'secret_state_code';

$browser_url = $oauth->getAuthorizeUrl(VK\OAuth\VKOAuthResponseType::CODE, $client_id, $redirect_uri, $display, $scope, $state);