QuickAuth is an implement of authorization(not a standard). By using QuickAuth, you can log in to some websites without sign up for another account, which most likely will be used only once. Frankly speaking, only my websites would use this platform.(hahah)
You don't have to own a Google account, but when you access some Google products, you need one, right?
In short,information such as username, email, verified or not, and some personal information(granted by the user) can be accessed.
It is hard to answer in short, you can have a look at this.
If you leave state blank in OAuth, this is kind of an implement of OAuth (code), but do not following that standrd especially the format of data exchanged.Learn more