longsleep@mose2:~$ snapcraft register-key longsleep1
Enter your Ubuntu One SSO credentials.
Email: simon@longsleep.org
Password:

We strongly recommend enabling multi-factor authentication: https://help.ubuntu.com/community/SSO/FAQs/2FA

Login successful.
Registering key ...

You need a passphrase to unlock the secret key for
user: "longsleep1"
4096-bit RSA key, ID 61D617D5, created 2016-01-01

Key registration failed: The account-key-request assertion is not valid.