HOW TO: Force all logins for subsites to go througth the main site login


I am looking to force all users of subsites, to use the main site login, then redirect to their correct dashboard.

For example, if a user tries to login on the, they are forced to login via the

There is a chat over here about it, and a MOD posted a plugin from 2013 :

Is there a simple way to do this?

My setup is:

WP 4.7.3 – Subdomains

WPMU – Domain Mapping