logging – Is it possible to differentiate devices connected to the same router in nginx logs?

We have a web server running nginx and a Rails app. Our logs have this format:

log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

However, I would like to be able to differentiate if two requests with the same IP come from different devices or the same one.
I suspect one person is connecting from the same device using two different users in two different browsers, and therefore, different user agents and different session cookies.

Is there any way to log a device ip or identifier?