Password for redirecting user to custom store

This is how my client wants their e-commerce site made. They are a supplier who want their customers to be able to use their site to order items that are unique to the specific customer.

They want to have an input bar on the home page where the user enters a password. Depending on which password is entered, they will be directed to a store page with items available only to them.

For example, John Doe is given the password “JD123”, which he can enter on the site. He is then redirected to a page that lists all of the items he can order for his business. Ann Smith is given the password “AS321”, which she can enter to see items that she can order. John is not able to see items available in Ann’s store and Ann is not able to see items available in John’s store.

What would be the best way to make this happen? I am looking at a few plugins but am having trouble tying them together.