CORS Handler for Akka Web Module

CORSHandler.scala

package ng.lep.web.routes

import akka.http.scaladsl.model.HttpMethods._
import akka.http.scaladsl.model.headers.{
  `Access-Control-Allow-Credentials`,
  `Access-Control-Allow-Headers`,
  `Access-Control-Allow-Methods`,
  `Access-Control-Allow-Origin`
}
import akka.http.scaladsl.model.{ HttpResponse, StatusCodes }
import akka.http.scaladsl.server.Directives.{ complete, concat, options, respondWithHeaders }
import akka.http.scaladsl.server.{ Directive0, Route }

trait CORSHandler {

  private val corsResponseHeaders                          = List(
    `Access-Control-Allow-Origin`.*,
    `Access-Control-Allow-Credentials`(true),
    `Access-Control-Allow-Headers`("Authorization", "Content-Type", "X-Requested-With")
  )
  //this directive adds access control headers to normal responses
  private def addAccessControlHeaders: Directive0 = {
    respondWithHeaders(corsResponseHeaders)
  }
  //this handles preflight OPTIONS requests.
  private def preflightRequestHandler: Route               = options {
    complete(
      HttpResponse(StatusCodes.OK).withHeaders(
        `Access-Control-Allow-Methods`(OPTIONS, POST, PUT, GET, DELETE)
      )
    )
  }
  // Wrap the Route with this method to enable adding of CORS headers
  def corsHandler(r: Route): Route                         = addAccessControlHeaders {
    concat(preflightRequestHandler, r)
  }
  // Helper method to add CORS headers to HttpResponse
  // preventing duplication of CORS headers across code
  def addCORSHeaders(response: HttpResponse): HttpResponse =
    response.withHeaders(corsResponseHeaders)

}