proxy=http://10.44.208.10:8080
proxy_username=username
proxy_password=password

[root@cp-hj-dev-gs02 ~]# yum update
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=6&arch=x86_64&repo=os error was
14: PYCURL ERROR 22 - "The requested URL returned error: 407"
Error: Cannot find a valid baseurl for repo: base

Linux cp-hj-dev-gs02 2.6.32-431.el6.x86_64 #1 SMP Fri Nov 22 03:15:09 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux