For you to ask for the password when opening NGFW, just edit the device settings you want to change, leaving the "password" field blank, leaving only the "User" field configured. After saving settings without the password field, when performing the next NGFW access via GSM, the same will ask for authentication for access to the graphical interface.
OBS: After saving settings, the device will be unavailable for GSM access for a few seconds to save the new configuration