a hash of auth tokens */ public function fetchAuthToken(callable $httpHandler = null); /** * Obtains a key that can used to cache the results of #fetchAuthToken. * * If the value is empty, the auth token is not cached. * * @return string a key that may be used to cache the auth token. */ public function getCacheKey(); /** * Returns an associative array with the token and * expiration time. * * @return null|array { * The last received access token. * * @type string $access_token The access token string. * @type int $expires_at The time the token expires as a UNIX timestamp. * } */ public function getLastReceivedToken(); }