Newscoop\Entity\User::generateRandomString PHP Method

    public final function generateRandomString($length = 12, $allowed_chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789')
    {
        $return = '';
        for ($i = 0; $i < $length; $i++) {
            $return .= $allowed_chars[mt_rand(0, strlen($allowed_chars) - 1)];
        }
        return $return;
    }

 /**
  * Generate user action token
  *
  * @param Newscoop\Entity\User $user
  * @param string $action
  * @return string
  */
 public function generateToken(User $user, $action = 'any')
 {
     $token = $user->generateRandomString(self::TOKEN_LENGTH);
     $this->em->persist(new UserToken($user, $action, $token));
     $this->em->flush();
     return $token;
 }