Not able to add repo when APT is using a proxy connection

Question

I have ubuntu 12.10 working on my system. I have tried many time to add repo but every time i tried i got the same error as in this case.

$ sudo add-apt-repository ppa:scopes-packagers/ppa
Cannot access PPA (https://launchpad.net/api/1.0/~scopes-packagers/+archive/ppa) to get PPA information, please check your internet connection.

my net is working fine. apt-get install is also working.

so why is it giving error that check your internet connection? ( i am working under proxy server with authentication)

$ cat /etc/apt/apt.conf file

Acquire::http::proxy "http://username:password@172.31.100.29:3128/";
Acquire::https::proxy "https://username:password@172.31.100.29:3128/";
Acquire::ftp::proxy "ftp://username:password@172.31.100.29:3128/";
Acquire::socks::proxy "socks://username:password@172.31.100.29:3128/";

Answer 1

This problem was solved in a thread in the Ubuntu forums. Look here and scroll to the bottom.

Answer 2

Only set http_proxy env variable is not enough. https_proxy is also required.

And I was needed to execute the add-apt-repository command as root, NOT via sudo. i don't know why it is not working with sudo but as root is working fine..