To configure bower behind a proxy, create a ".bowerrc" file in root of your project.
{
"directory": "bower_components",
"registry": "http://bower.herokuapp.com",
"proxy":"http://<USERNAME>:<PASSWORD>@<PROXY_IP>:<PROXY_PORT>/",
"https-proxy":"http://<USERNAME>:<PASSWORD>@<PROXY_IP>:<PROXY_PORT>/"
}