$ie = New-Object -Com "InternetExplorer.application"
$ie.Navigate("https://anav-rt.acs.whcaas.com")
while($ie.Busy){Start-Sleep -Milliseconds 100}
$doc = $ie.Document
$doc.getElementsByTagName("input") | % {
    if($_.name -ne $null){
        if($_.name.Contains("txtUsername")){ $user = $_ }
        if($_.name.Contains("txtPassword")){ $pass = $_ }
        if($_.name.Contains("btnLogin")){$btn = $_ }
    }
}

$user.value = "wallboard"
$pass.value = "OH NO YOU DONT"
$btn.click()
$ie.Visible = $true