app/filters/HstsFilter.scala

package filters

import org.apache.pekko.stream.Materializer
import play.api.mvc.{Filter, RequestHeader, Result}

import scala.concurrent.{ExecutionContext, Future}

class HstsFilter(implicit material: Materializer, ec: ExecutionContext)
    extends Filter {
  def apply(
      next: RequestHeader => Future[Result]
  )(header: RequestHeader): Future[Result] = {
    next(header).map(
      _.withHeaders("Strict-Transport-Security" -> "max-age=31536000")
    )
  }

  override implicit def mat: Materializer = material
}