I have deployed Ceph with Juju. I am trying to ssh in with the following command:

sam@maas01:~$ sudo juju ssh ceph/0

Permission denied (publickey,password).

error: exit status 255

I have my public key in /home/sam/.ssh/. I had also tried to explicitly specify the key's path in enviornments.yaml file which didn't help.
And as I had seen in many posts not to add ssh keys in MAAS web panel, I haven't added they key there. Any help?