Membership website with keys

I want to turn my website into a membership website with multiple membership levels. Users will be promoted from one level to another using keys or codes that I will provide them. Also, they will have to enter a new key every month to mantain their level, otherwise they will be demoted to the base level.

What I want to do is pretty much like a subscription membership website where people pay a monthly fee to keep their membership premium, but instead of paying money, my users will have to enter a key or code and will be promoted automatically and demoted if they don’t enter a new key every month.

How can I accomplish this? I have looked trough a lot of membership plugins paid and free but I couldn’t find one that can do this, but I guess there should be a way or combination of plug-ins that can do this.