AWS S3 offers a feature to enable server-side encryption of files.  
If I understand correctly, this is enabled by sending a specific HTTP header with the request to upload the file in question.   
So, this header needs to be set every time we want to upload a new file.  

Is this feature already supported / being considered for future versions?

If not, am I correct in assuming it would have to be implemented in https://github.com/joeyh/git-annex/blob/master/Remote/S3.hs ?

Thank you
