Variation of https://alexn.org/snippets/2020/08/27/safe-password.scala.html using cats-effect concurrency primitives.

SafePassword.scala

final case class PasswordValue(value: String) {
  override def toString = "PasswordValue(****)"
}

object SafePassword {
  def resource[F[_]: Sync](value: String): F[Resource[F, PasswordValue]] =
    for {
      used <- Ref.of[F, Boolean](false)
      chars = value.toCharArray
      givePasswordAndNullify = Sync[F].delay {
        val s = new String(chars)
        for (i <- chars.indices)
          chars(i) = 0
        PasswordValue(s)
      }
      illegalState = Sync[F].raiseError[PasswordValue](
        new IllegalAccessException(
          "the data has already been used once"
        )
      )
      validateState = Sync[F].delay(assert(chars.forall(_ == 0)))
      res = Resource.make(
        used
          .getAndSet(true)
          .ifM(illegalState, givePasswordAndNullify)
      )(_ => validateState)
    } yield res
}