implement notification system to avoid polling requests

[Ricardo Kirkner]

Currently, the only way a consumer has to know whether account creation has completed is to periodically poll the API for the status of the user's account.

By implementing a notification system, this polling could be avoided, and SSO would just notify the consumer when the process completed.

An implementation could be via a message queue (rabbitmq) where consumers would subscribe to sso messages.

By exposing different kind of events via this queue, other types of requests could also be avoided (for example, requesting tokens and checking whether they are still valid can be skipped, as the consumer would be notified every time a new token is created and invalidated).

This queue could also be used to expose a logout notification so that the user could get logged out of all the subscribing systems simultaneously.