How can I customize the error messages (such as \"These credentials do not match our records.\") that are displayed upon unsuccessful login/registration without
You don't want to override the getFailedLoginMessage() method in AuthController. The proper solution is to change the message in the designed location. If you look in the Resources > lang > en folder, you will see an auth.php file. In it, there is a "failed" attribute with a message you can customize. Change it there. The orignial getFailedLoginMessage() method in the Laravel auth files in vendor looks to that location for a custom message first, before settling on the default.