Internet Proxy authentication in Ubuntu

How to solve "407 Proxy Authentication Required" error in Ubuntu ?

This was one question i was behind from last few days.  Use CNTLM , that's the best answer I got.
CNTLM will make your ubuntu server act as a proxy server and in behind authenticates with your actual proxy server .

Step 1:  Download the package file from the CNTLM website . While writing this, version 0.92.3 is the latest and the link to it is http://citylan.dl.sourceforge.net/project/cntlm/cntlm/cntlm%200.92.3/cntlm_0.92.3_i386.deb

Step 2: Install .deb file . See How to install .deb files in Ubuntu here

Step 3:  cntlm configuration file is located at /etc/cntlm.conf . Open it using your preferred text editor in edit mode . If you use gedit , type " sudo gedit /etc/cntlm.conf "

Step 4:  In cntlm.conf ,  edit the following fields

    Username   YOUR_USERNAME_HERE
    Domain     YOUR_ORGANIZATION_DOMAIN(Contact your Active Directory admin if you don't knw this)
    Password YOUR_PASSWORD
    Proxy  YOUR_PROXY_SERVER_IP_WITH_PORT
    NoProxy LIST_ALL_IP_WITH_NO_PROXY_REQUIREMENT
    Listen SOME_PORT

Sample config here:

   Username   0906895
   Domain     ABC
   Password   rndmpasswd@123
   Proxy  10.18.200.203:8080
   Proxy  10.18.200.204:8080
   NoProxy  localhost, 127.0.0.*, 10.*
   Listen  8080

Step 5:  After changes in configuration files, restart the cntlm service .
 sudo service cntlm restart

Now cntlm started working and your ubuntu server is acting as another proxy server . So add localhost as the system proxy server.

System Proxy setting:

Go to System -> Preference -> Network Proxy
In the Network Proxy Preference window,  Set Manual proxy configuration . Proxy server as localhost and port as the port number you specified in " Listen SOME_PORT" .