CleanupChallengeFile not called and files are left uncleaned

[wuzhuoqing]

I am seeing challengeFile left under the acme folder. Seems CleanupChallengeFile is not called any where? Is this expected?
KuduFileSystemAuthorizationChallengeProvider even doesn't have a implementation.

letsencrypt-siteextension/LetsEncrypt.SiteExtension.Core/Services/KuduFileSystemAuthorizationChallengeProvider.cs

Line 26 in 6b9f2e1

return Task.CompletedTask;