code: def get_canonical_user_id(self, headers=None):
          
          rs = self.get_all_buckets(headers=headers)
          return rs.ID
docs: Convenience method that returns the "CanonicalUserID" of the
          user who's credentials are associated with the connection.
          The only way to get this value is to do a GET request on the
          service which returns all buckets associated with the account.
          As part of that response, the canonical userid is returned.
          This method simply does all of that and then returns just the
          user id.
  
          :rtype: string
          :return: A string containing the canonical user id.