The Jake Group

The purpose of this plugin is to facilitate deployment of subdomain links to 
landing pages on a WordPress website. The plugin automatically maps subdomains 
to page and post permalinks based on the post_name field in the database. 
There are no administrative settings.
This plugin DOES NOT edit DNS zone files. Subdomain DNS records themselves 
either need to be set up individually or as a wildcard record in the DNS zone 
file to map to the website directory. Once the request reaches the WordPress 
system, the plugin will automatically check to see if the subdomain matches a 
page or post name. If so, the WordPress query is edited to get that page/post 
at its permalink. The WordPress siteurl is excluded, as is the naked 
second-level domain.
Example mappings:
URL → Mapping 
http://example.com → default homepage (no remapping) 
http://www.example.com → default homepage (no remapping) 
http://test-page.example.com → example.com/test-page/ 
http://mypost.example.com → example.com/mypost/

Automatic Subdomains

Automatically maps subdomains to page and post permalinks based on post slug.

Scott Kingsley Clark

linickx

If you want to integrate the wordpress authentication magic into another script within your website you may come across authentication issues because your code cannot read the wordpress cookie.
By default the wordpress cookie exactly matches the URL of your installation, this plugin removes any subfolders from the cookie so that your whole domain has access to it.
For Example if you have wordpress installed in http://www.mydomain.com/wordpress/ any php stored in http://www.mydomain.com/mymagiccode/ cannot see the cookie due to browser security. This plugin changes the path to http://www.mydomain.com/ so that any php code on your site can access the cookie, so in our above example http://www.mydomain.com/mymagiccode/checkauthentication.php can now check the cookie to see if you have logged into wordpress.
NEW: Now you can allow cookies to be used across subdomains! Here are some examples that you can now access cookies from:
<ul>
<li>http://www.mydomain.com/</li>
<li>http://test.mydomain.com/</li>
<li>http://www.mydomain.com/blog/</li>
<li>http://test.mydomain.com/new/</li>
<li>http://forum.mydomain.com/getwordpresslogin.php</li>
</ul>
<h3>Multi-blog Installs</h3>
It is possible to use this plugin such that if you are logged into one WordPress site, then you are auto-magically logged into the second, but there are some caveats!
<ol>
<li>The Username & Password MUST be the same on Both!</li>
<li>The Security Keys https://codex.wordpress.org/Editing_wp-config.php#Security_Keys Need to be the same on Both!</li>
</ol>
<h3>Support</h3>
Comments on my website are welcome, but please post <a href="https://wordpress.org/tags/root-cookie?forum_id=10#postform" rel="ugc">in this WordPress Forum</a>

root Cookie

Even after so much time since the last update, your plugin worked perfectly and helped me fix my website. Thank you so much!!

THANK YOU!!

Changes the cookie default path to / (i.e. the whole domain.com not just domain.com/blog) with an option to go across subdomains

Automatic Subdomains vs root Cookie