In airflow’s configuration file `airflow.cfg` what is the `secret_key`, and do I have to set it?

As a comment above the value, it says # Secret key used to run your flask app, but that doesn’t tell me much. Currently it is set to secret_key = temporary_key, but that seems unsafe. We have set up password protection on the webservice, and it is backed by postgres running on Ubuntu 14/16.