Introduction for FTS transfers with tokens

• basic draft sent by FTS team to wlcg-doma-bdt email group
• discussed related question about storage support for renaming files
  • normal for disk storage, but not so common for TAPE
    • no rename on CTA, name or path is used to decide which tape to use
    • dCache use PNFSID for TAPE - no change during file rename
    • StoRM?
  • also not common for object storage
    • rename would require a copy of data
• decouple token support in two independent steps (Brian)
  • step 1: start with powerful tokens with delete (may be even delete whole storage)
  • step 2: reduce token privilege
    • make special upload area and atomic rename
    • failed transfers could be safely cleaned
  • CMS suggestion
    • one token per RSE with storage.modify
    • avoid temporary staging areas