CoroutineContext

class MyElement : CoroutineContext.Element {
    override val key: CoroutineContext.Key<*>
        get() = MyElement

    companion object : CoroutineContext.Key<MyElement>
}

fun main() {
    embeddedServer(Netty, host = "0.0.0.0", port = 12345) {
        sendPipeline.intercept(ApplicationSendPipeline.Before) {
            withContext(coroutineContext + MyElement()) {
                proceed()
            }
        }

        sendPipeline.intercept(ApplicationSendPipeline.Transform) {
            println(coroutineContext[MyElement])
        }

        routing {
            get("/") {
                call.respondText { "OK" }
            }
        }
    }.start(wait = true)
}