Unhelpful error from AccountKeyHandler if account assertion does not exist

[Simon Eisenmann]

I cannot register any key with my store account. As suggested in #snappy IRC channel i just file this bug to snapcraft until a better place for it is found or created.

longsleep@mose2:~$ snapcraft login
Enter your Ubuntu One SSO credentials.
Email: <email address hidden>
Password:

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

Login successful.
longsleep@mose2:~$ snap login <email address hidden>
Password:
Login successful
longsleep@mose2:~$ snapcraft keys
    Name SHA3-384 fingerprint
- longsleep1 BBZk-RcyZ-tJN9eRJTW-pwcHg7r2ME-Bm9kUn5qOKyRQMJ9SPyrham_UHoSNnrAJ
  (not registered)

longsleep@mose2:~$ snapcraft register-key longsleep1
Enter your Ubuntu One SSO credentials.
Email: <email address hidden>
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.

[Colin Watson (cjwatson)]

The problem was that the account was lacking an account assertion. We believe we've fixed up all the affected accounts, but SCA could have issued a more helpful error message here.