This quest hints that a key is needed to open the citadel. It asks for Orbs of Luclinite to make a new key.
I have not found any orbs yet, however, I did try the door and got:
"The forces within the Courtyard are blocking you from using this door."
"This is locked..."
"It's locked and you're not holding the key."
However, the door opens and I can enter.