Implement AuthService and ApiClient core logic

Models/UserModels.cs

@@ -0,0 +1,11 @@
+using Newtonsoft.Json;
+
+namespace Chtn.CSharp.SDK.Models.User
+{
+    public class PersonalUserData
+    {
+        [JsonProperty("userid")] public string UserId { get; set; }
+        [JsonProperty("username")] public string Username { get; set; }
+        [JsonProperty("email")] public string Email { get; set; }
+    }
+}