Play: json headers

// Does Play Framework add Content-Type headers automatically?
import javax.inject.Inject
import play.api.libs.json.Json
import play.api.mvc._

class TestController @Inject() (
    cc: ControllerComponents,
  ) extends AbstractController(cc) {

  // add to routes: GET    /test/json    controllers.TestController.simpleJson
  def simpleJson = Action {
    Ok(Json.obj("key" -> 5, "value" -> List(1, 2, 3)))
  }
}

// Call: http://localhost:9000/test/json
// Output: {"key":5,"value":[1,2,3]}
// Headers:
    Content-Length                        25
    Content-Security-Policy               default-src 'self'
    Content-Type                          application/json
    Date                                  Sun, 19 Aug 2018 19:17:51 GMT
    Referrer-Policy                       origin-when-cross-origin, strict-origin-when-cross-origin
    X-Content-Type-Options                nosniff
    X-ExampleFilter                       foo
    X-Frame-Options                       DENY
    X-Permitted-Cross-Domain-Policies     master-only
    X-XSS-Protection                      1; mode=block