Do doors provide any cover at all?

I ask this since when moving soldiers directly in front of a door, no Shield icon shows up that would let you know how much cover you have. I know that alien troops can aimbot you and know where you are EVEN if the door is closed, but so far, they've missed every single shot against a soldier posted right behind a door.

Does this mean I'm on to something? Doors take a move action to be opened and closed, so I'm wondering if the door made any impact on me dodging bullets, or does it not matter what state the door is in, and I simply got lucky?

No, doors provide no cover. Once opened they remain opened even if closed.

I found this when playing a UFO mission and two soldiers either side of the UFO doorway. I opened the door to 'spawn' the enemies inside, which they did. Then I closed the door, hoping to limit their ability to hit me and force movement.

The next turn a Viper pulled one of my troops directly through the closed door with it's tongue attack, and ADVENT troops shot through the door at my other squad mates.