WordPress MultiSite Active Directory integration and site privacy

Try a different approach. Instead of using plugins, I suggest modifying wordpress a little as described in the following answer.

https://stackoverflow.com/a/39195424/3157038

So in your case you should setup the wordpress installations like this:

• mysite.com
  • root: */domains/mysite.com/public_html
  • db: user_mysite
  • table prefix: root_
• mysite.com/itsupport
  • root: */domains/mysite.com/public_html/itsupport
  • db: user_mysite
  • table prefix: itsupport_

than in addition to the configuration given in the answer which i linked to, add the following to the wp-config files of both the wordpress installations:

define( 'CUSTOM_USER_TABLE', 'mysite_users );
define( 'CUSTOM_USER_META_TABLE', 'mysite_usermeta' );