Thank you for your reply.
I wanted to choose between password authentication and non-authentication depending on the user, so I imagined the following SQL.
$conf['plugin']['authpdo']['check-pass'] = 'SELECT id AS "uid"
FROM user
WHERE login = :user
AND (pass = :hash
OR [some way to bypass authentication])';
However, I found this method difficult, so I decided to implement it by setting placeholders in the password form.