For starters: you should look up "LDAP Security" using your favorite search engine.
I will say I like the solution that crypto has come up with in the form of not being able to spend the same BTC twice. Something involving that and user verification would be ideal for online voting although those two are very different technologies. Luckily math has the answer.
Now, whether that will be a sustainable solution without any security issues is probably not realistic but you bring up an important point and something that needs attention not just in your domain but in other domains as well. Maybe "quantum" DNA verification and multifactor authentication…
