Initialize-WebClientProxyCredentials.ps1

<#
.SYNOPSIS
    Make a download with webclient using the DefaultNetworkCredentials to authenticate at proxy.
    Afterwards all new webclient based cmdlets can pass the proxy.

.DESCRIPTION
    Make a download with webclient using the DefaultNetworkCredentials to authenticate at proxy.
    Afterwards all new webclient based cmdlets can pass the proxy.

.EXAMPLE
    Just call to install credentials

    Initialize-WebClientProxyCredentials.ps1

.LINK
    http://blog.stangroome.com/2013/08/02/powershell-update-help-and-an-authenticating-proxy/
#>

 # make one download through proxy with authentication
 $wc = New-Object System.Net.WebClient
 $wc.Proxy.Credentials = [System.Net.CredentialCache]::DefaultNetworkCredentials
 $tmp = $wc.DownloadString('http://microsoft.com')

 Write-Host "Default network credentials are installed. You can  use other WebClient based clients" -ForegroundColor Green