fix(configuration-database): resolve ConfigurationDatabase-002..007 — remove hardcoded sa creds, fail-fast no-arg DI, encrypt secret columns, resilient audit serialization

src/ScadaLink.ConfigurationDatabase/Services/AuditService.cs

@@ -8,6 +8,19 @@ public class AuditService : IAuditService
 {
     private readonly ScadaLinkDbContext _context;
 
+    /// <summary>
+    /// Serializer options for audit <c>afterState</c> payloads. Audit writes commit in the
+    /// same transaction as the change they record, so a serialization exception here would
+    /// roll back the entire business operation. Reference cycles (common when an EF entity
+    /// with loaded navigations is passed in) are ignored rather than thrown, and depth is
+    /// bounded so a pathological graph cannot produce an unbounded payload.
+    /// </summary>
+    private static readonly JsonSerializerOptions AuditSerializerOptions = new()
+    {
+        ReferenceHandler = System.Text.Json.Serialization.ReferenceHandler.IgnoreCycles,
+        MaxDepth = 32
+    };
+
     public AuditService(ScadaLinkDbContext context)
     {
         _context = context ?? throw new ArgumentNullException(nameof(context));
@@ -26,7 +39,7 @@ public class AuditService : IAuditService
         {
             Timestamp = DateTimeOffset.UtcNow,
             AfterStateJson = afterState != null
-                ? JsonSerializer.Serialize(afterState)
+                ? SerializeAfterState(afterState)
                 : null
         };
 
@@ -34,4 +47,27 @@ public class AuditService : IAuditService
         // to ensure atomicity with the entity change.
         await _context.AuditLogEntries.AddAsync(entry, cancellationToken);
     }
+
+    /// <summary>
+    /// Serializes the caller-supplied after-state, tolerating arbitrary object shapes.
+    /// Reference cycles are ignored via <see cref="AuditSerializerOptions"/>. If serialization
+    /// still fails (e.g. <c>MaxDepth</c> exceeded), the audit entry is preserved with a
+    /// diagnostic placeholder rather than throwing — a serialization failure must never
+    /// roll back the business operation the audit entry is recording.
+    /// </summary>
+    private static string SerializeAfterState(object afterState)
+    {
+        try
+        {
+            return JsonSerializer.Serialize(afterState, AuditSerializerOptions);
+        }
+        catch (Exception ex) when (ex is JsonException or NotSupportedException)
+        {
+            return JsonSerializer.Serialize(new
+            {
+                AuditSerializationError = ex.Message,
+                StateType = afterState.GetType().FullName
+            });
+        }
+    }
 }