Parse enqueued mail message model to object (#1742)

* Parse enqueued mail message model to object

The model of an MailQueueMessage is of type object to enable enqueueing
of any message. However, this means the we are not able to parse a
serialized json object back into the original object.
Provide the model type to enable this deserialization

* Use ExpandoObject for deserialized queue message model

src/Core/Models/Mail/IMailQueueMessage.cs

@@ -9,6 +9,6 @@ namespace Bit.Core.Models.Mail
         IEnumerable<string> BccEmails { get; set; }
         string Category { get; set; }
         string TemplateName { get; set; }
-        object Model { get; set; }
+        dynamic Model { get; set; }
     }
 }

src/Core/Models/Mail/MailQueueMessage.cs

@@ -1,4 +1,6 @@
 using System.Collections.Generic;
+using Newtonsoft.Json;
+using Bit.Core.Utilities;
 
 namespace Bit.Core.Models.Mail
 {
@@ -9,11 +11,12 @@ namespace Bit.Core.Models.Mail
         public IEnumerable<string> BccEmails { get; set; }
         public string Category { get; set; }
         public string TemplateName { get; set; }
-        public object Model { get; set; }
+        [JsonConverter(typeof(ExpandoObjectJsonConverter))]
+        public dynamic Model { get; set; }
 
         public MailQueueMessage() { }
 
-        public MailQueueMessage(MailMessage message, string templateName, object model)
+        public MailQueueMessage(MailMessage message, string templateName, dynamic model)
         {
             Subject = message.Subject;
             ToEmails = message.ToEmails;

src/Core/Utilities/ExpandoObjectJsonConverter.cs

@@ -0,0 +1,19 @@
+using System;
+using System.Dynamic;
+using Newtonsoft.Json;
+
+namespace Bit.Core.Utilities
+{
+    public class ExpandoObjectJsonConverter : JsonConverter
+    {
+        public override bool CanWrite => false;
+        public override bool CanConvert(Type objectType) => true;
+
+        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+        {
+            return serializer.Deserialize<ExpandoObject>(reader);
+        }
+
+        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) => throw new NotImplementedException();
+    }
+}