I’m curious, how can a database be accessed without authorization? If authorization is enabled? Also how unauthorized access can be discovered? Say I use Mongodb and enabled authorization. Will I be fine then? How to discover unauthorized access?
Authorization has a common English definition too. If, for example, an employee's credentials were compromised, anyone who wasn't that employee who accessed the database would be considered "without authorization". And checking the access logs for any use of that employee's credentials would give you some idea of what data was accessed. Enabling authorization on your mongodb is good, but it absolutely won't stop all forms of unauthorized access. They may gain access to your server itself, or gain some credentials to your MongoDB database some other way (for example, if someone carelessly ships them as part of your software, or includes them in a github commit, or something like that).
In the worst case, if someone notifies you of a configuration problem or some software bug that allows anonymous access to your database or the ability to remove logs, you may have to assume the entire database was compromised since the existence of that configuration issue or software bug.