Community Auth

1) Community Auth only calls $this->load->database(); and make no attempt to choose a database or any connection settings. Those are all part of CodeIgniter's database configuration, which means that Community Auth is just using the default database connection. If your specific application uses the MEDIA database by default, then unless your override the _load_dependencies method in Auth_Controller, your Community Auth related tables would need to be added to that database.

2) The way you are extending base controllers should work just fine, although you haven't shared any code so it's just an assumption.

3) Are you using multiple databases?

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Community Auth For CodeIgniter 3