The app opens an SSH session here and forwards a random local port to MySQL on the server (see appsettings.json → SshTunnel: default remote 127.0.0.1:3306). MySQL is not contacted on the public internet.
appsettings.json
SshTunnel
127.0.0.1:3306
Credentials for MySQL on the remote host (after the tunnel), same as in MySQL Workbench when connected through SSH.