Create and save a new request token.

        :param request: OAuthlib request.
        :type request: oauthlib.common.Request
        :param credentials: A dict of extra token credentials.
        :returns: The token as an urlencoded string.

def create_request_token(self, request, credentials):
        """Create and save a new request token.

        :param request: OAuthlib request.
        :type request: oauthlib.common.Request
        :param credentials: A dict of extra token credentials.
        :returns: The token as an urlencoded string.
        """
        token = {
            'oauth_token': self.token_generator(),
            'oauth_token_secret': self.token_generator(),
            'oauth_callback_confirmed': 'true'
        }
        token.update(credentials)
        self.request_validator.save_request_token(token, request)
        return urlencode(token.items())