WaitForCallback.kt

val code = suspendCancellableCoroutine { continuation ->
    val server = HttpServer.create(InetSocketAddress(5789), 0)

    server.createContext("/callback") { http ->
        val parameters = http.requestURI.query?.let { decodeQueryString(it) }
        val code = parameters?.get("code") ?: throw RuntimeException("Received a response with no code")

        sendResponse(http)

        continuation.resume(code)
    }
}