Lock, unlock or refresh the lock of a file. Requires read-write permission on the parent folder. Locked files cannot be modified by other users.

• lock: optional expire = lock duration in seconds (0 = server default). Fails with 400 File is locked if the file is already locked.
• unlock: allowed for the lock owner, the library owner and library admins.
• refresh-lock: only for the lock owner; optional expire (>= 0).