yii\authclient\OAuth1::fetchRequestToken PHP Method

    public function fetchRequestToken(array $params = [])
    {
        $this->setAccessToken(null);
        $defaultParams = ['oauth_consumer_key' => $this->consumerKey, 'oauth_callback' => $this->getReturnUrl()];
        if (!empty($this->scope)) {
            $defaultParams['scope'] = $this->scope;
        }
        $request = $this->createRequest()->setMethod($this->requestTokenMethod)->setUrl($this->requestTokenUrl)->setData(array_merge($defaultParams, $params));
        $this->signRequest($request);
        $request->setContent('');
        // enforce empty body, avoiding duplicate param server error
        $response = $this->sendRequest($request);
        $token = $this->createToken(['params' => $response]);
        $this->setState('requestToken', $token);
        return $token;
    }

 /**
  * @return string
  * @throws Exception
  */
 public function getAuthorizationUri()
 {
     if ($this->service instanceof OAuth1) {
         $token = $this->service->fetchRequestToken();
         $authorizationUri = $this->service->buildAuthUrl($token);
     } elseif ($this->service instanceof OAuth2) {
         $authorizationUri = $this->service->buildAuthUrl();
     } else {
         throw new Exception(Yii::t('SyncSocial', 'SyncSocial is not support {serviceName}.', ['serviceName' => get_class($this->service)]));
     }
     return $authorizationUri;
 }