/**
* Gets the google OAuth access token.
*
* @throws \Widop\GoogleAnalytics\Exception\GoogleAnalyticsException If the access token can not be retrieved.
*
* @return string The access token.
*/
public function getAccessToken()
{
if ($this->accessToken === null) {
$headers = array('Content-Type' => 'application/x-www-form-urlencoded');
$content = array('grant_type' => 'assertion', 'assertion_type' => 'http://oauth.net/grant_type/jwt/1.0/bearer', 'assertion' => $this->generateJsonWebToken());
$response = json_decode($this->httpAdapter->postContent($this->url, $headers, $content));
if (isset($response->error)) {
throw GoogleAnalyticsException::invalidAccessToken($response->error);
}
$this->accessToken = $response->access_token;
}
return $this->accessToken;
}
