Say that a figure opens a door. Can it later be closed by either the Rebels or the Imperials (perhaps with the intention of blocking line of sight or hindering movement)?
Players cannot close doors after they are opened, only game effects can close an open doorway.
From the Rules Reference Guide (page 11 under Doors)
If an effect closes a door, place a door token on the map as shown on the mission’s map. Figures cannot voluntarily close doors.