Hi there,
This is way outside of the theme’s scope but to help you out:
This seems like a bad idea. You’re basically opening your site up to potential security risk.
Plus, it’s a bad structure. Some parts are not exactly practical since you’ll still have to authenticate which one user can submit on which post. It’s literally the same thing as asking someone to log in. You might as well do just that.
That said, it’s better to set the role permission of users that are post authors if your worry is that you don’t want them to be able to access admin menu settings on the backend.