I understand that security and privacy concerns are important, but there are many use cases where assigning a unique identifier to players is necessary. To solve some of the issues in this thread, I suggest that the server assigns a unique identifier to each player upon joining, which can be exposed in code, while keeping the username private.
Currently, I assign unique identifier numbers to players in my game, but I encounter issues when some players leave or new players join. (As my game doesnt use rounds) If the server assigns and exposes unique identifiers, keeping those identifiers for returning players and keeps a real-time list or array of players, it would be very beneficial.