The password field is not required. You can use the email verification feature instead.
The login information for the portal users is stored on a base in your Airtable account. You should avoid maintaining sensitive credentials in your Airtable base. We recommend that you use a pin field for login, instead of a password. Or in some cases, the login fields could be a combination of personally identifiable info. E.g. name, birthdate, phone number, address, etc. This way you will ensure that you don't access their password.