<html>
<body onLoad="document.forms['sendparams'].submit();" >
<form name="sendparams" method="POST" action="$url_to_action_page" enctype="application/x-www-form-urlencoded" >
<input type="hidden" name="username" value="$username">
<input type="hidden" name="password" value="$password">
</form>
</body>
</html>