public function createToken($userId)
 {
     $token = Strings::createRandomString(null, Strings::ALPHABET_ALPHANUMERICAL, 512);
     $this->setUserId($token, $userId, true);
     return $token;
 }
 /**
  * Generates an identifier for a document.
  *
  * @param \Doctrine\ODM\MongoDB\DocumentManager $dm
  * @param object $document
  * @return string
  */
 public function generate(DocumentManager $dm, $document)
 {
     return Strings::createRandomString(null, $this->alphabet, $this->bitStrength);
 }