Every so often we have a client worrying about unauthenticated users. For example, as part of the output of "SHOW PROCESSLIST" they will see:+-----+----------------------+--------------------+------+---------+------+-------+------------------+| Id | User | Host | db | Command | Time | State | Info |+-----+----------------------+--------------------+------+---------+------+-------+------------------+| 235 | unauthenticated user | 10.10.2.74:53216 | NULL | Connect | NULL | login | NULL || 236 | unauthenticated user | 10.120.61.10:51721 | NULL | Connect | NULL | login | NULL || 237 | user | localhost | NULL | Query | 0 | NULL | show processlist |+-----+----------------------+--------------------+------+---------+------+-------+------------------+Who are these unauthenticated users, how do they get there, and why aren't they authenticated?The client-server handshake in MySQL is a 4-step process. Those familiar with mysql-proxy already know these steps, as there are four functions that a Lua script in mysql-proxy can override. The process is useful to know for figuring out exactly where a problem is when something breaks.