def descriptor: Descriptor = {
    import Service._
    named("user").withCalls(
      restCall(Method.GET,    "/api/users",              getUsers _),
      restCall(Method.POST,   "/api/users",              createUser _),
      restCall(Method.GET,    "/api/users/:id",          getUser _),
      restCall(Method.DELETE, "/api/users/:id",          deleteUser _),
      restCall(Method.PUT,    "/api/users/:id/verify",   verifyUser _),
      restCall(Method.PUT,    "/api/users/:id/unverify", unVerifyUser _),
      restCall(Method.POST,   "/api/users/auth",         getUserAuth _),
      restCall(Method.POST,   "/api/users/auth/grant",   userLogin _),
      restCall(Method.POST,   "/api/users/auth/revoke",  revokeToken _),
      restCall(Method.POST,   "/api/users/auth/refresh", refreshToken _)
    )
  }

object UserSerializerRegistry extends JsonSerializerRegistry {
  override def serializers = ...

  private val emailAdded = new JsonMigration(2) {
    override def transform(fromVersion: Int, json: JsObject): JsObject = {
      if (fromVersion < 2) {
        json + ("email" -> JsString("[email protected]"))
      } else {
        json
      }
    }
  }

  override def migrations = Map[String, JsonMigration](
    classOf[CreateUser].getName -> emailAdded,
    classOf[UserCreated].getName -> emailAdded,
    classOf[UserAggregate].getName -> emailAdded
  )
}

trait EmailService extends Service {
  def getEmails: ServiceCall[NotUsed, List[EmailResponse]]

  def emailEvents: Topic[EmailKafkaEvent]

  def descriptor: Descriptor = {
    import Service._
    named("email").withCalls(
      restCall(Method.GET, "/api/emails", getEmails _)
    )
      .withAutoAcl(true)
      .withExceptionSerializer(new DefaultExceptionSerializer(Environment.simple(mode = Mode.Prod)))
      .withTopics(topic("EmailEvents", emailEvents))
  }
}