Password protected premium content

Hey! I’ve got a question. I have a course store on an external site and after purchase the customer gets an access code. On the course platform, I want to make it so that before going to the page of the course he bought and seeing all its content, he has to enter this code to proceed. How to do it? I know, that it is possible to make a store and a platform with courses on one page and it would be easier, but this is the situation.