title: Corporate Github behind proxy: Received HTTP code 503 from proxy after CONNECT
body: <p>I am trying to clone from a corporate git repo, but always receive this error message after a while:</p>
  
  <p>fatal: unable to access URL: Received HTTP code 503 from proxy after CONNECT</p>
  
  <p>I have the following .gitconfig file:</p>
  
  <pre><code>[https]
      sslVerify = false
      proxy = https://proxy.corpadderess:8080
  [http]
      sslVerify = false
      proxy = http://proxy.corpadderess:8080  
  </code></pre>