We need the ability to unlock files via CSOM (with an App Only token) via the SPFile.ReleaseLock method. The flow would be similar to what we can accomplish on-prem:

$web = Get-SPWeb http://webUrl
$list = $web.Lists['Documents']
$item = $list.Items[0]
$lockId = $item.File.LockId
$item.File.ReleaseLock($lockId)

This prevents needing to open support cases for long-lived lock files in scenarios where the end user is having connectivity issues causing long exclusive locks to be created, potentially locking the end user out of their own file.