how to set tag or id for Exoplayer MediaSource?

Question

I am using Exoplayer for playing multiple audio files.

We can set media an Id when creation using:

MediaItem.Builder()
   .setUri(uri)
   .setMediaId("my_unique_id")

and get media Item id in onMediaItemTransition listener using mediaItem.mediaId.

val playerListener = object : Player.Listener {


    override fun onMediaItemTransition(mediaItem: MediaItem?, reason: Int) {
        super.onMediaItemTransition(mediaItem, reason)
        val id =  mediaItem?.mediaId
    }

in my use case, I must use MediaSource instead of MediaItem. how can I set media source a tag or id and get it in onMediaItemTransition?