Running chocolatey behind an authenticating firewall

I long grappled with a problem installing applications using chocolatey. Specifically, all installations that required downloading an MSI (or similar) file outside the .nupkg caused the following error message:

The remote server returned an error: (407) Proxy Authentication Required.

Yes, I am behind a firewall that requires authentication. I found several references to this error message on the chocolatey forums, but they all seemed to be fixed in the latest chocolatey version.

Through some googling I was able to track down the problem. Acutally, it is a problem with the .NET 3.5 runtime that causes the System.Net.WebClient to give up on an NTLM authentication challenge from proxies. Chocolatey uses Powershell, and indeed the System.Net.WebClient to download installation packages (all though not the package manifest itself, where it uses NuGet). As you my or may not know, Powershell uses the .NET 3.5 runtime per default.

Hence, the fix was to make Powershell use the .NET 4.0 runtime, where this bug is fixed. I figured out how to do this based on this entry on stackoverflow.

I then wrote this little Powershell snippet which changes Powershell on my machine to use .NET 4.0 instead of .NET 3.5:

if ([Environment]::Version.Major -lt 4) {
	$configFile = Join-Path $PSHOME -ChildPath '.powershell.exe.config'
	if (-not(Test-Path $configFile)) {
		@'
<?xml version="1.0"?>
<configuration>
  <startup useLegacyV2RuntimeActivationPolicy="true">
    <supportedRuntime version="v4.0.30319" />
    <supportedRuntime version="v2.0.50727" />
  </startup>
</configuration>
'@ | Out-File -FilePath $configFile -Encoding UTF8
		"Created $configFile"
	}
	'Restart powershell in order to make it run in .NET 4'
}