How to connect to Mysql proxy?

I want to use MySQL proxy for read/write splitting and load balancing for the Master/Slave replications.

I installed MySQL Proxy in one of the servers. I can login using admin-username and admin-password. My question is how to login MySQL Proxy like a normal client user? I did not set any client username and password in the configuration file. Also how MySQL Proxy connect to My database server (proxy-backend-addresses)? I did not provide any user/password information in the configuration file.

[mysql-proxy]
#daemon = true
admin-address = 10.61.247.1:4041

plugins=proxy,admin

log-file                                = /var/log/mysql-proxy.log
log-level                               = debug
proxy-address = 10.61.247.1:4040
proxy-read-only-backend-addresses = 10.42.40.2:3306
proxy-backend-addresses = 10.42.40.3:3306
proxy-lua-script=/usr/local/mysql-proxy-0.8.5-linux-glibc2.3-x86-64bit/rw-splitting.lua

admin-username=root
admin-password=testpassword
admin-lua-script=/usr/local/mysql-proxy-0.8.5-linux-glibc2.3-x86-64bit/admin.lua

Edit

Now I can use MySQL client to login using 10.42.40.3's username and password. I can not login using 10.42.40.2's username and password.

Please advise!

mysql --host=10.61.247.1 --port=4040 -uusername -p