We cannot automatically log in to the embedded form in the portal due to security issues that may arise. However, there is a workaround to achieve the same result.
In the form, go to the Table & Login section and get the login formula.
In the users table you use for your portal, create a formula field and paste the values here.
Go to the portal configuration.
Locate the Menu Item section
In the menu item in which you want to embed the form, use Airtable Field in Menu Item URL Type and select the newly created formula field.
By using this setup, you will achieve the same result of having users automatically logged in to the embedded form in the portal.
The same applies if you are embedding a portal within a portal.
Submitting an embedded form will not update the portal automatically, since the two are entirely separate. This means that any record you submit through the form will not show up in the portal until you manually refresh the page! If you want to create new records in your portal table, we strongly recommend using the "Create Records" functionality of the portal itself!