Write Submitting User's Department Upon Form Submission

I'm new to PowerApps and am customizing a SharePoint list form.  When the user submits the form, I need it to look up their department in AD and then write that into a department field on the form.  Is that possible?  I see that I can replace the form's function for OnSave, but I've no idea how to do the look up.

As a side question, even though the form is writing the value, it will still show that the user modified the list record, correct?  I currently am using Flow to do the lookup and write in the department, but it shows my account as modifying the field, which causes issues for our auditing.