Called to return the ticket for a request.

        Args:
            request: aiohttp Request object.

        Returns:
            A ticket (string like) object, or None if no ticket is available
            for the passed request.

async def get_ticket(self, request):
        """Called to return the ticket for a request.

        Args:
            request: aiohttp Request object.

        Returns:
            A ticket (string like) object, or None if no ticket is available
            for the passed request.
        """
        session = await get_session(request)
        return session.get(self.cookie_name)