Say I type in my wifi password and press "Remember" or something. It should store it, either as a hash or plain text, in a file somewhere.
- Where is that file?
- Is it stored as a hash or plain text?
If you are using normal settings on Raspbian it will be in
/etc/wpa_supplicant/wpa_supplicant.conf. It is stored in plain text, but only
root can see it - you will need
sudo to access the file.
See How do I set up networking/WiFi/Static IP for more detail.