Asp Net Core Web Push Notifications

The node library you mention has been ported to c#: web-push-csharp.

Here’s a simplified usage example taken directly from their site:

var pushEndpoint = @"https://fcm.googleapis.com/fcm/send/efz_TLX_rLU:APA91bE6U0iybLYvv0F3mf6uDLB6....";
var p256dh = @"BKK18ZjtENC4jdhAAg9OfJacySQiDVcXMamy3SKKy7FwJcI5E0DKO9v4V2Pb8NnAPN4EVdmhO............";
var auth = @"fkJatBBEl...............";

var subject = @"mailto:example@example.com";
var publicKey = @"BDjASz8kkVBQJgWcD05uX3VxIs_gSHyuS023jnBoHBgUbg8zIJvTSQytR8MP4Z3-kzcGNVnM...............";
var privateKey = @"mryM-krWj_6IsIMGsd8wNFXGBxnx...............";

var subscription = new PushSubscription(pushEndpoint, p256dh, auth);
var vapidDetails = new VapidDetails(subject, publicKey, privateKey);

var webPushClient = new WebPushClient();
try
{
    webPushClient.SendNotification(subscription, "payload", vapidDetails);
}
catch (WebPushException exception)
{
    Console.WriteLine("Http STATUS code" + exception.StatusCode);
}