Added User credential authentication

Models/JSON/Login.cs

@@ -0,0 +1,19 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Newtonsoft.Json;
+using System.Threading.Tasks;
+
+namespace EFB.Models.JSON
+{
+    public class Login
+    {
+        [JsonProperty]
+        public string grant_type { get; set; }
+        [JsonProperty]
+        public string client_id { get; set; }
+        [JsonProperty]
+        public string client_secret { get; set; }
+        
+    }
+}

Models/JSON/LoginResponse.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Newtonsoft.Json;
+
+namespace EFB.Models.JSON
+{
+    public class LoginResponse
+    {
+        [JsonProperty]
+        public string access_token { get; set; }
+        [JsonProperty]
+        public int expires_in { get; set; }
+        [JsonProperty]
+        public string token_type { get; set; }
+        [JsonProperty]
+        public string scope { get; set; }
+        
+
+        [JsonProperty]
+        public string error { get; set; } = null;
+        [JsonProperty]
+        public string error_description { get; set; } = null;
+        
+        
+    }
+}