Authentication required (packagist.org) Laravel instalation

I'm using ubuntu 16.04 and trying to install laravel (any version). Actually i cloned from github the laravel project (http://ift.tt/UDctZi) After cloning I'm running the command as below

root:/var/www/html/laravel$ composer install Loading composer repositories with package information Updating dependencies (including require-dev) Authentication required (packagist.org): Username: This is the issue i'm facing, i don't know what username i have to give, and why its asking authentication.. And if i run composer diagnose the below code was coming

composer diagnose Checking composer.json: OK Checking platform settings: OK Checking git settings: OK Checking http connectivity to packagist: Authentication required (packagist.org): Username: Any suggestions or can anyone tell what was i'm missing here

via Chebli Mohamed