I'm glad Efficy doesn't store any password - from users or contacts - in plain text or in a reversible way.
Note that the stored passwords are not encrypted, they are salted and hashed. This is much more secure.
Short said, you can't reproduce this unsecure behavior in 11+ versions, you will have to add e-mails into the flow. This is the common behavior for accessing a personalized section on web applications.
In a guest request, the contact is identified using the unique
mailingcode. If the contact has already an extranet account, you can redirect the browser to the logon page. The person can use his browser to store the credentials or a password utility.
If the person does not have an extranet account, ask in the guest page if Efficy should send a password renewal e-mail. After the password is set, the user will be redirected to the extranet logon page.