code: public function getAccessToken($oauthToken, $oauthVerifier)
      {
          //Oauth1 plugin to get access tokens!
          $oauth = new Oauth1(array(
              'consumer_key'    => $this->credentials->getConsumerKey(),
              'consumer_secret' => $this->credentials->getConsumerSecret(),
              'token'           => $oauthToken,
              'verifier'        => $oauthVerifier
          ));
  
          //attach oauth to request
          $this->guzzleClient->getEmitter()->attach($oauth);
  
          //POST to 'oauth/access_token' - get access tokens
          $accessTokenResponse = $this->guzzleClient->post(
              Config::get('oauth_access_token'),
              array(
                  'auth' => 'oauth'
              )
          );
  
          //handle response
          $response = array();
          parse_str($accessTokenResponse->getBody(), $response);
  
          //set access tokens
          $this->credentials
              ->setAccessToken($response['oauth_token'])
              ->setAccessTokenSecret($response['oauth_token_secret']);
  
          return $response; //contains 'oauth_token', 'oauth_token_secret', 'user_id' and 'screen_name'
      }
docs: Get Access tokens from the user in exchange of oauth_token and oauth_verifier and return
  them.
  
  @param  string $oauthToken
  @param  string $oauthVerifier
  @return array contains 'oauth_token', 'oauth_token_secret', 'user_id' and 'screen_name'.