Parses app key from betfair exchange site.

        :param requests.session session: Requests session object

def login(self, session=None):
        """
        Parses app key from betfair exchange site.

        :param requests.session session: Requests session object
        """
        session = session or self.client.session
        try:
            response = session.get(self.login_url)
        except ConnectionError:
            raise APIError(None, self.login_url, None, 'ConnectionError')
        except Exception as e:
            raise APIError(None, self.login_url, None, e)
        app_key = re.findall(r'''"appKey":\s"(.*?)"''', response.text)
        if app_key:
            self.app_key = app_key[0]
        else:
            raise RaceCardError("Unable to find appKey")