I'm working on a project that involves multi-sites in Drupal 8. The client specifically wants to have shared user accounts across all 4-5 sites. As of now the sites share a codebase but not a shared database. After researching I came across the CAS module. Can CAS allow for multiple logins? When one account is made can other accounts be generated in the other 3-4 Drupal sites? Is there a better way to do this in Drupal 8? Also, the client eventually wants to have paid account registries. For example, a user would pay on one site and get access to all 4-5 sites. IS there any guidance for accomplishing this? If not with CAS what other modules / resources would I need to make this doable in Drupal 8?
So far I've seen sites that offer advice on this but largely with Drupal 7 with out a clear path for doing this in Drupal 8. CAS seemed the most stable option but not sure if it will work. There was also the option of sharing users through shared tables, though this was discouraged in the forums I read. What is the best / proper way to do this in Drupal 8? Or should I go back to Drupal 7?