Login to view API keys

Sign in with the account's email address and password. The reply holds the account and its API keys. A wrong password and an unknown address get the same 401 (code: invalid_login). The right password for an address that has not been confirmed yet gets 403 code: email_not_confirmed, and a new confirmation link is sent. Repeated wrong passwords for one address are held back with code: login_backoff and retry_after_seconds. An account with two-factor sign-in gets two_factor_required: true and a challenge to complete on the website.