What is the best practice for identifying userTokens if a login is possible at any point in the customer journey?

If customers are able to log in to your site at any time, they may perform valuable user interactions (i.e. click and conversion events) before they've logged in. Then when they log in and complete their journey, some click and conversion events may be missing from their user profile. 

There are two options when considering how to implement userTokens, and they each have their own trade offs.

1. The first way is to assign their userToken as their login ID. The problem here is that if they log in after all of their clicks and conversions have been made, those initial events will not be tied to their userToken or user profile. 
2. The second way is to assign the userToken as the IP address of the user. This makes it so their userToken is the same throughout their entire journey, but it also means that if the user visits your site on a different device (i.e. a different IP), they will have a different userToken.

 
Another consideration is to offer the login page (either as a pop up or by some other method) right away to the user so the likelihood that they log in earlier is increased.