Android で gRPC通信 をする時に MetaData を使いたい！

class UserServiceClient{

    private val channel: ManagedChannel = ManagedChannelBuilder
            .forAddress(BuildConfig.SERVER_URL, BuildConfig.PORT.toInt())
            .useTransportSecurity()
            .build()

    private var userStub: UserServiceGrpc.UserServiceBlockingStub = UserServiceGrpc.newBlockingStub(channel)

    suspend fun user(sessionId: String) = coroutineScope {

        Metadata().apply {
            put(Metadata.Key.of("authorization", Metadata.ASCII_STRING_MARSHALLER), "session $sessionId")
        }.let {
            //  この，stubに代入してあげるのを忘れると積むので気をつけること！！
            userStub = MetadataUtils.attachHeaders(userStub, it)
        }

        val createRequest = Users.GetCurrentUserRequest.newBuilder()
                .build()

        userStub.getCurrentUser(createRequest)
    }
}