Keep students from Logging in with private Credentials

​For Chromebooks, we can lock them down to only domain (cps.edu) users, but unless you blacklist the add account pages, students can still add their personal accounts and do whatever they want. In the Admin Console you can blacklist URLs. To the best of my knowledge, these are the sites to blacklist (on student devices only, unless you want to upset your Chromebook using teachers):

https://accounts.google.com/AccountChooser
https://accounts.google.com/AddSession
Accounts.google.com/Log9out
Accounts.youtube.com/Logout2
Accounts.google.com/AddSession
https://accounts.google.com/AccountChooser
https://accounts.google.com/AddSession#identifier

Those should prevent the addition of personal accounts moving forward. The issue is that if they have all ready added that personal account, this actually blocks them from signing out of the personal account and will block them from their CPS accounts. At that point, you will have to instruct them to reset Profile Settings (chrome://settings/resetProfileSettings). That resets them back to default (it doesn't lose bookmarks, it just signs them out of everything). It is a pain, but it works. 

​-- Ron