有了.NET Core，您可以使用这个轻量级的library来发送FCM推送通知和APN HTTP/2推送通知：

Install-Package CorePush

然后是Firebase：

using (var fcm = new FirebaseSender(serverKey, senderId))
{
    await fcm.SendAsync(notification);
}

或APN：

using (var apn = new ApnSender(privateKey, keyId, teamId, appbundleId, server)) 
{
    await apn.SendAsync(deviceToken, notification);
}

有些人也喜欢这个问题，所以想到提供我实现的解决方案，认为它可能会帮助其他人。如果你有任何问题，请随时提问。

如何获取服务器密钥：这里是question link，它会有所帮助。
Firebase云消息传递文档可在here中找到。

public class FirebaseNotificationModel
{
    [JsonProperty(PropertyName = "to")]
    public string To { get; set; }

    [JsonProperty(PropertyName = "notification")]
    public NotificationModel Notification { get; set; }
}

using System.Net.Http;
using System.Text;
public static async void Send(FirebaseNotificationModel firebaseModel)
{
    HttpRequestMessage httpRequest = null;
    HttpClient httpClient = null;

    var authorizationKey = string.Format("key={0}", "YourFirebaseServerKey");
    var jsonBody = SerializationHelper.SerializeObject(firebaseModel);

    try
    {
        httpRequest = new HttpRequestMessage(HttpMethod.Post, "https://fcm.googleapis.com/fcm/send");

        httpRequest.Headers.TryAddWithoutValidation("Authorization", authorizationKey);
        httpRequest.Content = new StringContent(jsonBody, Encoding.UTF8, "application/json");

        httpClient = new HttpClient();
        using (await httpClient.SendAsync(httpRequest))
        {
        }
    }
    catch
    {
        throw;
    }
    finally
    {
        httpRequest.Dispose();
        httpClient.Dispose();
    }
}