async def process_request(
        self, request: Union[Request, HTTPConnection]
    ) -> Optional[Any]:
        """
        Runs always on request.

        Extracts value from header by default.
        """
        assert isinstance(self.key, str)
        return await self.extract_value_from_header_by_key(request)

        Runs always on request.

        Extracts value from header by default.
        
starlette_context/plugins/base.py