I have cleared all of the enemies in the area and I didnt find a key or anything to unlock the door. The optional objective to Free Brick is still there. I was thinking I could use a body to trick the door into opening but it still gives the same unauthorized message when I interact with it. How are you meant to get inside?
To the left of the door you will find a keypad. Standard buttons with a pin code kind of thing. I am not sure if the code is random or what but if you go into the room to the right you will find a computer on top of one of the glass display case things. In the messages of this computer you will find an email with the code to unlock the cage and free brick.
It may be randomly generated for every game but you can try using 9691 to unlock the door. Interact with the keypad and enter it. If it doesnt work, check the laptop in the room to the right and it will have the code for you here.