How to set the 'source address' ProxySQL uses to connect to MariaDB?

I'm deploying ProxySQL on Docker. When I try connecting to my database via ProxySQL, MariaDB rejected my login attempt as follows: Access denied for user 'usarr'@'172.18.0.1' (172.18.0.1 is the container's "internal" IP address.) The Docker host itself has LAN address of 192.168.9.22. And the user configured in MariaDB is 'usarr'@'192.168.9.%' How do I configure ProxySQL to connect as usarr@192.168.9.22? I've tried reading the (very confusing) documentation for ProxySQL and couldn't figure out how.