Add logging before and after placing an order through MAX.

Add logging after saving a batch.

BulkPrintingAPI/Controllers/BatchesController.cs

             credentials.User.Account.Balance = orderResponse.RemainingBalance;
             await _context.SaveChangesAsync();
 
+            _logger.LogDebug("Saved batchId={0} for {1}", orderResponse.Batch.Id, credentials.ToString());
+
             try
             {
                 await Utils.DownloadVouchersAsync(_sftpOptions, _context, _logger, orderResponse.Batch);

MAXClient/Client.cs

             var response = ExpectResponse(await ReadMessageAsync().ConfigureAwait(false), "Hi");
 
             // Request server RSA key
+            //
+            // WARNING:
+            //
+            // The protocol does not do any form of server authentication so this step is
+            // trivially vulnerable to a man-in-the-middle attack where an intermediary 
+            // intercepts this request and sends their own RSA key while keeping the server RSA
+            // key to themselves.
             await WriteMessageAsync(new MessageBuilder().Append("PK")).ConfigureAwait(false);
             response = await ReadMessageAsync().ConfigureAwait(false);
 
                 throw new ArgumentException("24 byte key expected", nameof(key));
             }
 
+            _logger.LogDebug(
+                "Placing order for {0}: date={1} quantity={2} productId={3} productDescription={4} networkId={5} networkName={6} customerRef={7} internalRef={8}",
+                LoginCredentials.Format(_userId, _username, _vendorId, _serialNumber),
+                DateTimeOffset.UtcNow,
+                quantity,
+                product.Id,
+                product.Description,
+                product.Network.Id,
+                product.Network.Name,
+                customerReference,
+                internalReference
+            );
+
             await WriteMessageAsync(new MessageBuilder()
                 .Append("Order ")
                 .Append(Encrypt(new StringBuilder()
 
             var response = ExpectResponse(Decrypt(await ReadMessageAsync().ConfigureAwait(false)), "OK");
 
+            _logger.LogDebug("Order response for {0} customerRef={1} internalRef={2}: {3}",
+                LoginCredentials.Format(_userId, _username, _vendorId, _serialNumber),
+                customerReference,
+                internalReference,
+                response
+            );
+
             var parts = response.Split('|');
             return new OrderResponse()
             {