Laravel: what is storage key in auth.php?

From API Authentication, it says

If you choose to use a different column name, be sure to update your API's storage_key configuration option within the config/auth.php configuration file.

I use token column instead if api_token name which is the default one for Laravel API authentication. It says config storage_key to use a different name. I can't find such thing and Googling this didn't say anything. What is storage_key and how can I use this to set the token as API authentication column name not api_token?

Thanks in advance

via Chebli Mohamed