Confirmation Form HTML?

Not long ago (6 months ago), I started learning Web Development on my own. I have come to a "limit" I cannot go beyond. So, here is the thing:

My client is asking me to make a website for his wedding where people can go and confirm that they will go. Now, he wants me to make a form (a rsvp form) what will take an specific code that was given to an specific guest to confirm their attendance. He wants to avoid other individuals trying to pass as invited-guests.

What should I do? At least, point me to the right direction. Any help is well appreciated.

Thanks!