Create a password restricted section to my site

I already have a site built in wordpress, i have installed a online booking calendar plugin, but i dont want just anyone to view this section of my site. I need to add a password page before they can see the calendar, Once a month i run a special discount offer to my database the offer is open for a week & people who purchase will get a voucher with a unique code giving them 1 year to book in. I would like if possible a way to upload a list of all the codes from those who have purchased & used the code & their surname as a cross check to allow them to see the calendar. I need it done straight away