def signup(username: String, password: String, teamIdOpt: Option[String], teamAuthTokenOpt: Option[String]): Option[Id[User]] = {
  val userIdOpt: Option[Id[User]] = getUserIdFromCredentials(username, password)

  (userIdOpt, teamIdOpt, teamAuthTokenOpt) match {
    case (Some(userId), Some(teamId), Some(authToken)) => joinTeam(userId, teamId, authToken)
    case _ =>
  }

  userIdOpt
}