New users are not created due to password integrity violation error

Please give more information about your Drupal installation, so I can investigate whether I want to do something about this vs. the other contrib/custom code that you have, should fix things.

Your SQL error shows a failing attempt to insert a recored in the user_pass table. Drupal Core has no user_pass table. So we need to know where that table comes from / what is using it.

Hi, yes, indeed this is our simple_password_policy module doing that. We hook into user_insert and user_update and save the existing
password hash into a table for lookup later (can't re-use the last x passwords).

pseudo code:
hook_user_insert($user) {
...
$pass = $user->getPassword(); => this returns empty value.
...
}

I think the reason is that in in SamlAuth service, ExternalAuth::register is called with
$account_data = ['name' => '...'];
which only contains a name and not containing a password.
Maybe a random password can be generated when the user is created ?
$account_data = ['name' => '...', 'pass' => '???'];

Rather than make samlauth accommodate simple_password_policy, simple_password_policy should IMHO accommodate the fact that passwordless users are a thing that exists in Drupal and is legal.

• Make PasswordPolicy::store() issue a DELETE instead of an INSERT/UPDATE if $user->getPassword() is empty. (The DELETE would also accommodate cases where $old_password is nonempty - which is very unlikely but it's not hard to implement just in case.)
• Make PasswordPolicy::applyPolicy() always return FALSE if $user->getPassword() is empty. After all, you don't want people to be issued warnings of passwords they don't have... which generating a random password would do.

Indeed, thanks for the suggestions!