Added filename to attachment and calculated attachment hash in subscriber

FitConnect/FluentSubscriber.cs

 using System.Buffers.Text;
 using System.Security.Authentication;
+using System.Security.Cryptography;
 using System.Security.Cryptography.X509Certificates;
 using FitConnect.Models;
 using FitConnect.Services;
@@ -107,8 +108,12 @@ public class FluentSubscriber : Subscriber, IFluentApi<FluentSubscriber> {
             var encryptedAttachment = SubmissionService.GetAttachment(Submission.Id, id);
 
             var content = Encryption.DecryptData(Convert.FromBase64String(encryptedAttachment));
-            // TODO Where to get the HASH from?
-            attachments.Add(new Attachment(id, content, "HASH"));
+            
+            // TODO where do I get the hash from the server to verify the attachment?
+            var hash = MD5.Create(HashAlgorithmName.SHA512.ToString())?.ComputeHash(content) ??
+                       Array.Empty<byte>();
+            
+            attachments.Add(new Attachment(id, content, Convert.ToBase64String(hash), "dummy.pdf"));
         }
 
         Submission.Attachments = attachments;

FitConnect/Models/Attachment.cs

 namespace FitConnect.Models;
 
-public record Attachment(string Id, byte[] Content, string Hash);
+public record Attachment(string Id, byte[] Content, string Hash, string Filename);