Generating unique random token using async Redis driver (https://github.com/debasishg/scala-redis-nb)

gistfile1.scala

def generateUniqueRandomToken(): Future[String] = {
  val token = generateRandomToken(TokenLength)
  redis.exists(tokenKey(token)) flatMap {
    case true  => generateUniqueRandomToken()
    case false => Future.successful(token)
  }
}

// ...

private val secureRandom = {
  val s = new SecureRandom
  s.nextInt()
  s
}

private val unreservedChars: Array[Char] =
  Array('-', '.', '_', '~') ++ ('0' to '9') ++ ('A' to 'Z') ++ ('a' to 'z')

private def generateRandomToken(length: Int) = {
  val chars = Array.fill(length) {
    val randIdx = secureRandom.nextInt(unreservedChars.length)
    unreservedChars(randIdx)
  }
  new String(chars)
}