I have a question regarding mixpanel.register_once. How does Mixpanel identify a web user without authentication? IP?
We manage identities with a property called distinct_id, and our client side SDKs will manage this for you by default.
In our JS SDK specifically, we use a random and unique 54-60 character hash that is stored in a cookie, rather than use an IP for security purposes.
You can read more about that here.
Hope this helps!