Website Client Area - Password Boxes

My wordpress themed site has a page which acts as a client portal. I have set it up with a number of password fields however there is currently no code behind the login boxes. I want to be able to access a designated Page within the website by entering a password into the relevant box. See attached. Once I am at the designated page, I don't want the URL for that designated page to be visible so that each time a person comes to the client area, they need to enter the password and proceed to the page to reach it (ie they can't just copy the URL otherwise it invalidates the need for this layer of protection/restriction). There will only be one password for each field and each page it goes to (i.e. I am not looking to establish passwords for users or anything like that - each page I navigate to via one of these password fields will have one single password). I want to be able to customise the password and once it is implemented for one of the password fields, I want to be able to lift that feature and cascade it to the other password boxes easily and customise a password for each of them to their respective page as the client area grows. The client area in question is on this website... [login to view URL]