First of all, the login experience should not change if the TOS is the same as before. If the TOS has changed, you could accept-reject the login (lock the cred

First of all, the login experience should not change if the TOS is the same as before. If the TOS has changed, you could accept-reject the login (lock the credentials in the fields) and say "to continue, please read the TOS change and press 'accept' to continue". Or just have this as a separate screen after the login.