$page = [
    'post_type' => 'page',
    'post_content' => '',
    'post_status' => 'publish',
    'post_title' => 'Create a new account',
    'post_name' => 'account new'
];

$page_id = wp_insert_post($page);

<form method="post" id="new-account-form" action="/account-pending/">

public function get_account_pending()
{

    if (isset( $_POST['my_check_value'])) {
        $username =       $_POST['username'];
        $password =       $_POST['userpass'];
        $firstname =      $_POST['firstname'];
etc...

add_action( 'wp', array( &$this, 'get_account_pending' ) );

$this
$_GET
$_REQUEST
$_SERVER
$GLOBALS