src/Google/Client.php
public function fetchAccessTokenWithAuthCode($code)
  {
    if (strlen($code) == 0) {
      throw new InvalidArgumentException("Invalid code");
    }

    $auth = $this->getOAuth2Service();
    $auth->setCode($code);
    $auth->setRedirectUri($this->getRedirectUri());

    $httpHandler = HttpHandlerFactory::build($this->getHttpClient());
    $creds = $auth->fetchAuthToken($httpHandler);
    if ($creds && isset($creds['access_token'])) {
      $creds['created'] = time();
      $this->setAccessToken($creds);
    }

    return $creds;
  }
public function fetchAccessTokenWithAuthCode($code)
  {
    if (strlen($code) == 0) {
      throw new InvalidArgumentException("Invalid code");
    }

    $auth = $this->getOAuth2Service();
    $auth->setCode($code);
    $auth->setRedirectUri($this->getRedirectUri());

    $httpHandler = HttpHandlerFactory::build($this->getHttpClient());
    $creds = $auth->fetchAuthToken($httpHandler);
    if ($creds && isset($creds['access_token'])) {
      $creds['created'] = time();
      $this->setAccessToken($creds);
    }

    return $creds;
  }
Attempt to exchange a code for an valid authentication token.
Helper wrapped around the OAuth 2.0 implementation.

@param $code string code from accounts.google.com
@return array access token