extra validation on play json reads

validate.scala

import play.api.libs.json._
import scala.reflect.runtime.universe._

def checkedReads[T](underlyingReads: Reads[T])(implicit typeTag: TypeTag[T]): Reads[T] = new Reads[T] {

  def classFields[U: TypeTag]: Set[String] = typeOf[U].members.collect {
    case m: MethodSymbol if m.isCaseAccessor => m.name.decodedName.toString
  }.toSet

  def reads(json: JsValue): JsResult[T] = {
    val caseClassFields = classFields[T]
    json match {
      case JsObject(fields) if (fields.keySet -- caseClassFields).nonEmpty =>
        JsError(s"Unexpected fields provided: ${(fields.keySet -- caseClassFields).mkString(", ")}")
      case _ => underlyingReads.reads(json)
    }
  }
}