Using a custom runtime with `toWebHandler` and sharing a cache across requests can be a bit trick...

const makeHandler = (authSession: Session | null) =>
  RpcServer.toWebHandler(AuthRpcGroup, {
    layer: Layer.mergeAll(
      AuthRpcLive.pipe(
        Layer.provide(
          Layer.provideMerge(UserSessionService.layer(authSession), MainLive),
        ),
      ),
      RpcSerialization.layerJson,
      HttpServer.layerContext,
    ),
    memoMap: ServerRuntime.memoMap,
  });

export const POST = async (request: NextRequest) => {
  const handler = makeHandler(await getServerSession(authOptions));
  return await handler.handler(request);
};