The Safeword

One always needed passwords at Hogwarts. Harry never minded, but disliked Neville's sleeping in front of the common room door.
During the war, passwords were a matter of life and death. Each Order member had one to prove their identity...
By war's end, Harry was sick of passwords, of secrets and divisions.
During Eight Year, he stubbornly shared his password with everyone... and when Malfoy entered the Gryffindor common room, Harry invited him to play chess.
Now, with Draco, Harry tolerates one password. It unlocks pain... pleasure. He allows it because it doesn't express suspicion, but complete trust. His safeword.