title: The "https://packagist.org/packages.json" file could not be downloaded
body: <p>I want to install a package for a Laravel chat app I'm making. When running "composer require foo/bar" I got the following error in the terminal:</p>
  
  <pre><code>In RemoteFilesystem.php line 515:
  
  The "https://packagist.org/packages.json" file could not be downloaded: failed to open stream: Unable to find the socket transport "proxy_user_name" - did you forget to enable it when you configured PHP?
  </code></pre>
  
  <p>I'm using a VPN but it's still referring to my proxy  credentials which is supposed to not see because of the VPN. </p>
  
  <p>When running "composer diagnose" I get this:</p>
  
  <pre><code>Lolo@lolo:/media/lolo/project_path/project_name$ 
  composer diagnose
  Checking composer.json: OK
  Checking platform settings: OK
  Checking git settings: OK
  Checking http connectivity to packagist: WARNING
  
  [Composer\Downloader\TransportException] The "http://packagist.org/packages.json" file could not be downloaded: failed to open stream: Unable to find the socket transport "foobar" - did you forget to enable it when you configured PHP?
  
  Checking https connectivity to packagist: WARNING
  [Composer\Downloader\TransportException] The "https://packagist.org/packages.json" file could not be downloaded: failed to open stream: Unable to find the socket transport "foobar" - did you forget to enable it when you configured PHP?
  
  Checking HTTP proxy: FAIL
  [Composer\Downloader\TransportException] The "https://packagist.org/packages.json" file could not be downloaded: failed to open stream: Unable to find the socket transport "foobar" - did you forget to enable it when you configured PHP?
  
  Checking HTTP proxy support for request_fulluri: WARNING
  Unable to assess the situation, maybe packagist.org is down (The "http://packagist.org/packages.json" file could not be downloaded: failed to open stream: Unable to find the socket transport "foobar" - did you forget to enable it when you configured PHP?)
  
  Checking HTTPS proxy support for request_fulluri: WARNING
  
  Unable to assess the situation, maybe github is down (The "https://api.github.com/repos/Seldaek/jsonlint/zipball/1.0.0" file could not be downloaded: failed to open stream: Unable to find the socket transport "foobar" - did you forget to enable it when you configured PHP?)
  Checking github.com rate limit: FAIL
  
  [Composer\Downloader\TransportException] The "https://api.github.com/rate_limit" file could not be downloaded: failed to open stream: Unable to find the socket transport "foobar" - did you forget to enable it when you configured PHP?
  
  Checking disk free space: OK
  Composer version: 1.6.3
  PHP version: 7.2.7-0ubuntu0.18.04.2
  PHP binary path: /usr/bin/php7.2
  </code></pre>
  
  <p>What could be causing the error?</p>