use wp authentication in non-wp folder

I have a normal wp install under /blog/ on my domain. In /some-other-sibling-folder/ I want to use the same wp-login data. If someone is loged in, they can do stuff in this folder, else they can only view.

Is that possible? Is there any way to check if I’m loged in in the wp-system, even if I’m in a different folder?

domain.com
domain.com/blog/ <- here’s the wp
domain-com/other/ <- here I want to check if user is loged in in the folder above.