HTTPS actually CAN be configured via config file (at least in Play 2.4).
play.server.http.address=127.0.0.1
play.server.http.port=9000
play.server.https.address=127.0.0.1
play.server.https.port=9443
But be aware: This will only works in prod mode (deploying Play with "activator stage", "activator dist", etc.) but not in developing mode.
For developing mode you have to use "activator -Dhttp.port=9443" and "... -Dhttps.port=9443" on the command line like Maxim described.
Starting with Play 2.5 (not released yet) you will also be able to set the ports for development mode by adding
PlayKeys.devSettings := Seq("play.server.http.port" -> "9000")
PlayKeys.devSettings := Seq("play.server.https.port" -> "9443")
in your build.sbt (not the application.conf!)
Conclusio: With Play 2.5 you will be able to set the production ports in application.conf and the development ports in build.sbt. For now you have to use the command line options for dev mode.
Regards,
Matthias