Log in to the main site automatically

I am looking for a plugin that would automatically log the user to his/her website and also to the main website. I am looking for something similar to WP Multisite SSO.
The issue with Multisite SSO is that is logging the user to all the websites, and if you have a network with +1000 websites, the user would have to wait a few good minutes before the log in. Also, the user is redirected to the main page, instead of being redirected to the dashboard.

The reason I'm asking that under Pro Site plugin is because I want to sort a flow issue when using Pro Sites. When the user wants to Upgrade and clicks on the upgrade link, he's redirected to the main website - the pro sites page (site.com/premium-sites/?bid=XX). But, because he's not logged into the main website, he has to enter credentials again. For a better UX, I would like to remove this step.

Thank you for all your support

Regards,
Mario