ubuntu:
  image: tutum/ubuntu:latest
  ports:
    - 2222:22
  environment:
    - AUTHORIZED_KEYS="YOUR SSH PUBLIC KEY HERE"

ubuntu:
  image: tutum/ubuntu:latest
  ports:
    - 2222:22
  environment:
    - AUTHORIZED_KEYS=YOUR SSH PUBLIC KEY HERE

Remove misleading double quotes in stack file
Remove misleading double quotes in stack file

User needs to provide ssh pub key without double quotes.

If user leaves the double quotes, the resulting stack file is created in Tutum like below:

ubuntu:
  image: 'tutum/ubuntu:latest'
  environment:
    - 'AUTHORIZED_KEYS="YOUR SSH PUBLIC KEY HERE"'
  ports:
    - '2222:22'

Container deployment logs will then show (notice doubles quotes here):
2015-07-06T20:52:53.994433980Z => Adding public key to /root/.ssh/authorized_keys: "YOUR SSH PUBLIC KEY HERE"

And in the container, we can then see:

root@ubuntu-1:~# cat .ssh/authorized_keys 
"YOUR SSH PUBLIC KEY HERE"

Obviously (even with the correct ssh key), it will show something like "ssh-rsa AAAAB3NzaC..." (with double quotes). Consequence is user cannot login with provided ssh key as file content isnt properly formated.