Return and generate if required the lock for this request.

def lock(self) -> asyncio.Lock:
        """
        Return and generate if required the lock for this request.
        """

        if self.lock_key not in self.request.custom_content:
            self.request.custom_content[self.lock_key] = asyncio.Lock()

        return self.request.custom_content[self.lock_key]