驗證身分

	if ( isset ( $_REQUEST['action'] ) ) {
		// 預計要 login
		$action = $_REQUEST['action'];
		if ( $action == 'login' ) {
			$username = $_REQUEST['username'];
			$userpw   = $_REQUEST['userpw'];
			$userpw   = hash('sha256', $userpw );
			if ( $username != $userok ) {
				$error = 1;
				$msg = "帳號不對";
			} elseif ( $userpw != $pwok ) {
				$error = 2;
				$msg = "密碼不對";
			} else {
				$error = 0;
			}
		}
	}

<?php
	if ( $error == "0" ) {
		echo "歡迎登入";
	} else { 
		if ( isset ( $msg ) ) echo $msg;
?>
<form ... />
...
</form>
<?php  } ?>