I already have the official WP Social login plugin installed, and it works individually on two of my Multisite network sites (I'm using the same Facebook App Id and OA account for both).
However, this doesn't achieve SSO between sites that a user is a member of. I find they still need to log in to each site separately.
I've tried to make sense of your guide at: https://docs.oneall.com/services/implementation-guide/social-login/
... but I'm not really sure how much of it applies to Wordpress.
Would you please let me know which steps I need to take to get SSO going on WPMU?