Invites are an intermediate way between opening registrations completely and closing registrations completely.
By letting users invite other users to the server, an administrator exposes themselves again to the risk of abuse.
To combat that abuse more effectively, this module allows to store (outside of the user’s information) who created an invite which was used to create the user’s account.
With the plugin installer in Prosody 0.12 you can use:
sudo prosodyctl install --server=https://modules.prosody.im/rocks/ mod_invites_tracking
For earlier versions see the documentation for installing 3rd party modules