How to install and configure SSO or CAS for drupal?

Question

Drupal

How to install and configure SSO or CAS for drupal?
What is the salt.
There is a site and there is a subdomain.
You need to make one authorization for two sites.
So that one user could use his password and login to enter both the site and the subdomain)
And which is better SSO or CAS?
Help please, urgently needed) I will help as much as I can, whoever helps, that is not a big gift)))

Answer 1

Site and subdomain on the same server?
Under your own is it under what, login / password from some third system? Or do you want to be able to access a subdomain using the login and password from the main site?