No error id for username/password error returned from snapd

[Robert Ancell]

If you fail to authentication with snapd the response is:

{"type":"error","status-code":401,"status":"Unauthorized","result":{"message":"cannot get discharge macaroon from store: Provided email/password is not correct."}}

In comparison, if you provide valid credentials but need two factor you get the response:

{"type":"error","status-code":401,"status":"Unauthorized","result":{"message":"two factor authentication required","kind":"two-factor-required"}}

The latter response has a 'kind' field which a client can use to provide appropriate text / imagery to inform the user. The former response does not, and the message is inappropriately technical to show to a user.

[Robert Ancell (robert-ancell)]

Suggest solution - add a kind="email-password-incorrect" field.

[John Lenton (chipaca)]

In #1562 I'm returning a 400 with `invalid-auth-data` when e.g. the email provided is not valid (the value will describe the validation error in detail); a 401 with `login-required` will be returned by other unauthorised results (e.g. provided email/password is not correct.).

[Robert Ancell (robert-ancell)]

Fixed in snapd 2.12