public function authenticate()
    {
        $request_token = $this->oauth->getRequestToken($this->settings, $this->consumer, $this->token);

        $auth_url = $this->settings('auth_api_url').$this->settings('authentication_uri');
        $auth_url .= '?'.http_build_query(['oauth_token' => $request_token->key]);

        return $this->redirect->to($auth_url);
    }