with reference var1

This doesn't seem to work at all. I can't figure out the issue.

That's not how setting reference variables works. You must first specify which variable is a reference under the Parameters tab. You then access it using the below format.

So in this case it would be the following.

How do I auto login and then redirect after the user completes sign up of the CB Subs plan instead of showing the thank you page.

There isn't a trigger available for the CBSubs thank you page so that's not really possible without risking interrupting other CBSubs processes. onCPayDisplayBasketResult would be the trigger to use. You'd need to check that the basket is completed. Example as follows.

Global
Triggers: onCPayDisplayBasketResult
User: Automatic
Access: Everybody
Conditions
Field: Custom > Value
Custom Value: [var1_payment_status]
Operator: Equal To
Value: Completed

var1 for this trigger is the payment basket object itself. It'll contain all the data that the _cbsubs_payment_baskets has. To try and log the user in during this you can try the following.

Global
Triggers: onCPayDisplayBasketResult
Type: Login / Logout
User: Automatic
Access: Everybody
Conditions
Field: Custom > Value
Custom Value: [var1_payment_status]
Operator: Equal To
Value: Completed
Action
Mode: Login
Method: User ID