Authenticate a user by POSTing with username and password. A status is returned, and if the status is login_successful, a token will be included. This token must be included for the Authentication of every subsequent API request (see "Authorization"). A user_id is also returned, which may need to be used in other API requests.

Possible statuses:

• login_successful (with token and user_id)
• error_missing_key
• error_account_disabled
• error_account_does_not_exist (for both missing accounts and bad password)
• error_non_post_request
• error_trial_expired
• error_account_delinquent