Cookie based authentication

[joepio]

See https://github.com/atomicdata-dev/atomic-data-docs/pull/138/files#

Browser issue

• Check out actix_identity
• Parse the cookie header, get the Authentication Resource. Use the cookie API, probably.
• Check (re-use get_agent_from_auth_values_and_check, extend it where needed)
  • if the signature matches
  • expires-at
  • if the subject matches (in this case, the server_url)