How to makepages that each client can see will be different?

Basically the biggest challenge will be to create a client login with a user name and password. Then some pages will only be visible by clients that are logged in. In addition, the pages that each client can see will be different. This is a medical practice that will be opening up in September. They will have weight loss clients and anti-aging clients and each group will have different pages that they can see.

Can this be achieved?
I know that there is code out there for client login, but page access differences?

I am guessing there should be.

[No bumping, please.]