Returns True if the OTP is valid (status=OK) and return_response=False,
        otherwise (return_response = True) it returns the server response as a
        dictionary.

        Throws an exception if the OTP is replayed, the server response message
        verification failed or the client id is invalid, returns False
        otherwise.

def verify_response(self, response, otp, nonce, return_response=False):
        """
        Returns True if the OTP is valid (status=OK) and return_response=False,
        otherwise (return_response = True) it returns the server response as a
        dictionary.

        Throws an exception if the OTP is replayed, the server response message
        verification failed or the client id is invalid, returns False
        otherwise.
        """
        try:
            status = re.search(r'status=([A-Z0-9_]+)', response) \
                       .groups()

            if len(status) > 1:
                message = 'More than one status= returned. Possible attack!'
                raise InvalidValidationResponse(message, response)

            status = status[0]
        except (AttributeError, IndexError):
            return False

        signature, parameters = \
            self.parse_parameters_from_response(response)

        # Secret key is specified, so we verify the response message
        # signature
        if self.key:
            generated_signature = \
                self.generate_message_signature(parameters)

            # Signature located in the response does not match the one we
            # have generated
            if signature != generated_signature:
                logger.warn("signature mismatch for parameters=%r", parameters)
                raise SignatureVerificationError(generated_signature,
                                                 signature)
        param_dict = self.get_parameters_as_dictionary(parameters)

        if 'otp' in param_dict and param_dict['otp'] != otp:
            message = 'Unexpected OTP in response. Possible attack!'
            raise InvalidValidationResponse(message, response, param_dict)

        if 'nonce' in param_dict and param_dict['nonce'] != nonce:
            message = 'Unexpected nonce in response. Possible attack!'
            raise InvalidValidationResponse(message, response, param_dict)

        if status == 'OK':
            if return_response:
                return param_dict
            else:
                return True
        elif status == 'NO_SUCH_CLIENT':
            raise InvalidClientIdError(self.client_id)
        elif status == 'REPLAYED_OTP':
            raise StatusCodeError(status)

        return False