Fetch the OAuth request token. Only required for OAuth 1.0.

def get_request_token(self, request, callback):
        """Fetch the OAuth request token. Only required for OAuth 1.0."""
        callback = force_text(request.build_absolute_uri(callback))
        try:
            response = self.request('post', self.request_token_url, oauth_callback=callback)
            response.raise_for_status()
        except RequestException as e:
            logger.error('Unable to fetch request token: {0}'.format(e))
            return None
        else:
            return response.text