v20 MAIN_SECURITY_SALT is undefined

[JonBendtsen]

about security page says:

MAIN_SECURITY_SALT = Undefined
The recommended value for MAIN_SECURITY_HASH_ALGO is now 'password_hash' but setting it now will make ALL existing passwords of all users not valid, so update is not possible.
If you really want to switch, you must:
- Go on home - setup - other and add constant MAIN_SECURITY_HASH_ALGO to value 'password_hash'
- In same session, WITHOUT LOGGING OUT, go into your admin user record and set a new password
- You can now logout and login with this new password. You must now reset password of all other users.

I wish this could be a environment variable (or secret) that I could set for new installations, or possibly something randomly generated which is stored in a permanent file or in the database? Nah