docs: def get_session(self, account_id):
          """Get an active session in the target account."""
          if account_id not in self.account_sessions:
              if account_id not in self.config['accounts']:
                  raise AccountNotFound("account:%s is unknown" % account_id)
  
              self.account_sessions[account_id] = s = assumed_session(
                  self.config['accounts'][account_id]['role'], "Sphere11")
              s._session.user_agent_name = "Sphere11"
              s._session.user_agent_version = "0.07"
          return self.account_sessions[account_id]