This allow the administrator define which Login portal types are searched, instead rely exclusively on ERP5 Login (hardcoded value).
A use case:
On SlapOS Master, an additional portal type was introduced (Certificate Login) which contains the CN of an SSL Certificate. Certificate Login is only usable as external login, independently if the user has login or not.
And certificate login is password less, so it cannot be used as a normal login.
WIP: I still need to check for tests.