If you are using Windows authentication, you could enable single sign on and it wouldn't be necessary for the user to manually log in.

Laserfiche Scanning is not a standalone application. It needs either a desktop or web client connection to the repository. I'm guessing you are launching the scanning application using a custom URL? That needs an active web client connection. If there isn't one, the user will be prompted to authenticate. The Forms user is irrelevant for the purposes of this connection.