Token authentication with webdav

[sverhoeven]

To authenticate against SURFSara's dCache servers a token (Macaroon) is needed. At the moment the Xenon webdav adaptor only accepts username/password combi. It would be nice if Xenon was able to copy files to/from a dCache webdav server using a token instead of username/password.

[sverhoeven]

Instead of using slower non-file transfer operations of webdav, we could create a dCache adapter which uses the dCache REST API for quicker operations. See https://github.com/sara-nl/SpiderScripts for cli client which use curl to talk to API.