Thanks to you.
Sorry for my english, with "custom form field (not persistent string type)" I mean "custom form property type", not stored on database, in addition to the form property types already supported (i.e string, long …).
You understand correctly the use case.
The alternative you described (SSO integration) is correct, and that's what we will do in the second phase of the project with regard to authentication mechanisms.
In the first phase of the project, however, we need to use a temporary solution, and in any case the password of the mailbox from which the mails are read and taken attachments to be loaded into the repository, must not be stored on the database.
For this reason I was thinking of using a custom form property type to manage password value in a session object and not on the database.
Cheers
Claudio