online voting system - technologies

I'm thinking about creating a web app to run an online vote. I have a database with all the people who can vote but I am not sure about how can I make them log in, I mean what login items should I use for security. I was thinking about the name and an ID number as SSN, for example, but this informations can be found very easily.

Also, what technologies should I use to keep their vote unique and anonymous?

I'm still in the planning stage, so any information would be very useful !

Thanks !