Check page access abilities using ID only

Using PHP, I need to check if a particular user ID (or username) has access to a specific post/page that is protected by S2Member. The user is not ‘logged in’, I have checked the credentials on a previous page to ensure it is being accessed through authorized means. I just need to know how to check page/post access only using ID; all of the S2Member functions I’ve found rely on a “current_user” context which is nonexistent in this case. How can I check page/post authorization/access using only a user ID?

https://wordpress.org/plugins/s2member/