Refactored S3 using AWS library and update with new filer API

I wonder if there is a better way to do this so we don't have to ask for the list.  Can we store a value at the keyPrefix (e.g., the date/time that it was created), so that for a user `foo` you can ask for the `foo` key and it's either there or not.  Or will this mess up because we use it as a prefix for other keys (i.e., can it be both)?