Hey Phillip,
So I was able to create a screen that works for what you're looking to do. Start by looking at what fields are required to create a portal. Next create a table with those fields on it. At this point you would build a screen from this table and add in your login information for the users you want to have access. Having a grid on the screen will allow you to view users you have already entered into the table. When you are setting up your portal, point it to the table you have just created. Now when they try and login, the portal will look at this table to authenticate the users.
Things to think about are;
Figure out how you’re going to associate these users with the company information. This will require a filter of some kind.
Unless the users email is on the table you created, they will not be able to login.
Everyone’s email must be unique or they will not be able to login.
This should help you out