How to make Multisite global login that redirects to correct subsite after login

I just tested this on my local with a fresh subdmoain setup. Here’s my setup:

• Created subdomain.test
• Added site: demo1.subdomain.test with the admin user demo1
• Added site: demo2.subdomain.test with the admin user demo2

Now, if I go to http://subdomain.test/wp-login.php and login, I get the following results:

• User demo1 logs in to http://subdomain.test/wp-login.php and is redirected to http://demo1.subdomain.test/wp-admin/
• User demo2 logs in to http://subdomain.test/wp-login.php and is redirected to http://demo2.subdomain.test/wp-admin/

In short, WordPress already does this for you, assuming that the admin users for your subdomains are only admins for those sites.