bash uses standard UNIX users, using the your OS’s authentication method(s).
Explaining that is out of scope here.
When you use a user/password with ssh or a console command to log into Karaf console, that’s a Karaf user.
Authentication will be matched against Karaf config. You can change password or put in a SSH key for that, see this thread.
There’s an openhabian menu option for that (except for the Karaf user I think).