@defer.inlineCallbacks
    def _check_recaptcha(self, authdict, clientip):
        try:
            user_response = authdict["response"]
        except __HOLE__:
            # Client tried to provide captcha but didn't give the parameter:
            # bad request.
            raise LoginError(
                400, "Captcha response is required",
                errcode=Codes.CAPTCHA_NEEDED
            )

        logger.info(
            "Submitting recaptcha response %s with remoteip %s",
            user_response, clientip
        )

        # TODO: get this from the homeserver rather than creating a new one for
        # each request
        try:
            client = self.hs.get_simple_http_client()
            resp_body = yield client.post_urlencoded_get_json(
                self.hs.config.recaptcha_siteverify_api,
                args={
                    'secret': self.hs.config.recaptcha_private_key,
                    'response': user_response,
                    'remoteip': clientip,
                }
            )
        except PartialDownloadError as pde:
            # Twisted is silly
            data = pde.response
            resp_body = simplejson.loads(data)

        if 'success' in resp_body and resp_body['success']:
            defer.returnValue(True)
        raise LoginError(401, "", errcode=Codes.UNAUTHORIZED)
dataset/ETHPy150Open matrix-org/synapse/synapse/handlers/auth.py/AuthHandler._check_recaptcha