There are plenty of ways to generate a one-off random seed for values used in the quizzes. And many of them don't require me to authenticate to the site; as others suggested, a cookie could be used, or even just a querystring value in the URL.

And promiscuously asking to connect social accounts to random things on the internet, even if they swear up and down that they don't request "undue" privileges, trains people to just always do it, which sets them up to get owned later on by someone who will take advantage of that.