Open the Sitecore in experience Editor Mode and add login in the Main section while log out rendering in Header section as shown below.
Add the Associated items(Login and Logout) under given item path as shown below.
These data source items are useful in order to customise the label, Error Message and Redirection Url post successful login as shown below.
Alright look like all set; let's see how its works in preview mode. Voila, it works perfectly fine as shown below.
Isn't it too easy?
Alright time to do deep dive to find the clue the crux is here.
My deep love with latest crush Sitecore SXA continues :)
Happy Sitecore Experience Acceleration.