Use the same login credentials with different core versions I have a Drupal 7 site, and I createda  new Drupal 8 site. I would like to use the login credential from the Drupal 7 site in the Drupal 8 site.

How can I achieve this?
You could set up the existing Drupal 7 site as an OAuth provider and then set up the Drupal 8 site to allow for OAuth logins and then you could share credentials between the sites.

You won't get any sync for free but at least you wouldn't have to enter the password again.