Function register_post_handler 

fn register_post_handler<P, F, Fut>(
    handlers: &mut Handlers,
    route: &str,
    func: F,
    is_authenticated: bool,
    router: Router,
) -> Router
where
    P: DeserializeOwned + Send + 'static,
    F: Fn(Extension<Arc<Gateway>>, Json<P>) -> Fut + Clone + Send + Sync + 'static,
    Fut: Future<Output = Result<Json<Value>, GatewayError>> + Send + 'static,

Registers a POST API handler for both the HTTP server and the Iroh Endpoint.