Added push notification class

Notification/PushNotification.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Net.Http;
+using System.Text;
+using System.Threading.Tasks;
+using Firebase.Xamarin.Auth;
+
+namespace Firebase.Xamarin.Notification
+{
+  public class PushNotification
+  {
+    private const string NotificationUrl = "https://fcm.googleapis.com/fcm/send";
+
+    private readonly FirebaseConfig authConfig;
+
+    public PushNotification(FirebaseConfig authConfig)
+    {
+      this.authConfig = authConfig;
+    }
+
+    public async Task Send(string to, string title, string message)
+    {
+      using (HttpClient client = new HttpClient())
+      {
+        var postContent = $"{{\"to\":\"{to}\",\"notification\":{{ \"title\":\"{title}\",\"text\":\"{message}\" }}}}";
+
+        client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("key", $"={this.authConfig.ApiKeyForPushNotification}");
+        var response = await client.PostAsync(NotificationUrl, new StringContent(postContent, Encoding.UTF8, "application/json")).ConfigureAwait(false);
+
+        response.EnsureSuccessStatusCode();
+      }
+    }
+  }
+}