Minecraft verification via website?

Is there maybe a plugin for Wordpress with which you can verify yourself in Minecraft?

So the idea is that there's a whitelist on the server, and if you enter your player name and e-mail address on a Wordpress website, you get on this whitelist.

I don't know anything like that and I don't think it exists either. You will probably have to have such special plugins programmed for you. Concerning worpdpress as well as Minecraft.