PHP+Apache实现二级域名之间共享cookie的方法

<VirtualHost 127.0.0.1:80>
  ServerName koastal.com
  ServerAlias www.koastal.com 
  DocumentRoot D:\wamp64\vhosts\www
  <Directory "D:\wamp64\vhosts\www">
    Options +Indexes +Includes +FollowSymLinks +MultiViews
    AllowOverride All
    Require local
  </Directory>
</VirtualHost>
<VirtualHost 127.0.0.1:80>
  ServerName login.koastal.com
  DocumentRoot D:\wamp64\vhosts\login
  <Directory "D:\wamp64\vhosts\login">
    Options +Indexes +Includes +FollowSymLinks +MultiViews
    AllowOverride All
    Require local
  </Directory>
</VirtualHost>

127.0.0.1  www.koastal.com login.koastal.com

<?php
if(isset($_COOKIE['username'])){
  echo "welcome to ".$_COOKIE['username'];
  var_dump($_COOKIE);
}else{
?>
<h1><a href='http://login.koastal.com'>Login</a></h1>
<?php
}

<form action="#" method="post">
<p>username:<input type="text" name="username"></p>
<p>password:<input type="password" name="password"></p>
<p><input type="submit" name="submit" value="submit"></p>
</form>
<?php
if(isset($_POST['submit'])){
  setcookie('username',$_POST['username'],0,'/','koastal.com');
  setcookie('password',$_POST['password'],0,'/','koastal.com');
  header('Location:http://www.koastal.com');
}