In order to help users complete the account creation flow efficiently, it would be good to verify if a username is available before the user submits the login form.
If possible, we should verify if a username is available after focus is taken off of the username field in the account creation flow.
The existing creation API can give us "Username already exists" as a result message, but we don't want to necessarily use the creation API as a "check" mechanism - i.e. it may be throttled to so many attempts or something - for example if the user tried 2 usernames and the server blocked them on the third attempt etc.
So for this spike determine if there is API support for checking if a user name exists.