#include <ie.au3>

Local $oUser, $oPass, $oSubmit
Local $sUser = "testuser"
Local $sPass = "abc123"
Local $url = "http://testingsite.com"
Local $oIE = _IECreate($url, 1)
Local $oInputs = _IETagNameGetCollection($oIE, "input")

_IELoadWait($oIE)

for $oInput in $oInputs
	if $oInput.type = "text" And $oInput.name = "username" And $oInput.size = "24" Then $oUser = $oInput
	if $oInput.type = "password" And $oInput.name = "password" And $oInput.size = "24" Then $oPass = $oInput
	if $oInput.type = "submit" And $oInput.value = "Submit" Then $oSubmit = $oInput
	if isObj($oUser) And isObj($oPass) And isObj($oSubmit) then exitloop
Next

$sUser.value = $sUser
$oPass.value = $sPass
_IEAction($oSubmit, "click")

_IELoadWait($oIE)