Add API key authentication middleware support

Introduced `ApiKeyAuthOptions` for API key configuration,
including a `Key` property and `SectionName` for binding.
Updated `ApiKeyAuthMiddleware` to validate the `X-Api-Key`
header against the configured API key.

Added conditional middleware application in `Program.cs`
based on the presence of a configured API key. Bound the
`ApiKey` section in `appsettings.json` and
`appsettings.Development.json` to store the API key, with
a default value of `null`. This improves security and
centralizes API key management.

src/presentation/DigitalData.TaskFlow.API/Middleware/ApiKeyAuthMiddleware.cs

@@ -1,6 +1,8 @@
 using DigitalData.TaskFlow.API.Contracts.Common;
+using DigitalData.TaskFlow.API.Options;
 using DigitalData.TaskFlow.Domain.Common;
 using DigitalData.TaskFlow.Domain.Enums;
+using Microsoft.Extensions.Options;
 using System.Text.Json;
 
 namespace DigitalData.TaskFlow.API.Middleware;
@@ -8,9 +10,10 @@ namespace DigitalData.TaskFlow.API.Middleware;
 /// <summary>
 /// Validates required API key header for API endpoints.
 /// </summary>
-public sealed class ApiKeyAuthMiddleware(RequestDelegate next)
+public sealed class ApiKeyAuthMiddleware(RequestDelegate next, IOptions<ApiKeyAuthOptions> apiKeyOptions)
 {
     private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web);
+    private readonly string? _configuredApiKey = apiKeyOptions.Value.Key;
 
     /// <summary>
     /// Executes middleware logic.
@@ -25,7 +28,7 @@ public sealed class ApiKeyAuthMiddleware(RequestDelegate next)
         }
 
         if (context.Request.Headers.TryGetValue("X-Api-Key", out var values)
-            && !string.IsNullOrWhiteSpace(values.FirstOrDefault()))
+            && string.Equals(values.FirstOrDefault(), _configuredApiKey, StringComparison.Ordinal))
         {
             await next(context);
             return;

src/presentation/DigitalData.TaskFlow.API/Options/ApiKeyOptions.cs

@@ -0,0 +1,8 @@
+namespace DigitalData.TaskFlow.API.Options;
+
+public sealed class ApiKeyAuthOptions
+{
+    public const string SectionName = "ApiKey";
+
+    public string? Key { get; init; }
+}

src/presentation/DigitalData.TaskFlow.API/Program.cs

@@ -96,6 +96,10 @@ try
         .AddOptions<SwaggerOptions>()
         .Bind(config.GetSection(SwaggerOptions.SectionName));
 
+    builder.Services
+        .AddOptions<ApiKeyAuthOptions>()
+        .Bind(config.GetSection(ApiKeyAuthOptions.SectionName));
+
     builder.Services.AddSerilogUi(options =>
     {
         options.UseSqliteServer(databaseOptions =>
@@ -110,11 +114,18 @@ try
     var swaggerOptions = app.Services
         .GetRequiredService<Microsoft.Extensions.Options.IOptions<SwaggerOptions>>()
         .Value;
+    var apiKeyOptions = app.Services
+        .GetRequiredService<Microsoft.Extensions.Options.IOptions<ApiKeyAuthOptions>>()
+        .Value;
 
     var enableSwagger = app.Environment.IsDevelopment() || swaggerOptions.EnabledInProduction;
+    var enforceApiKey = !string.IsNullOrWhiteSpace(apiKeyOptions.Key);
 
     app.UseMiddleware<ExceptionHandlingMiddleware>();
-    app.UseMiddleware<ApiKeyAuthMiddleware>();
+    if (enforceApiKey)
+    {
+        app.UseMiddleware<ApiKeyAuthMiddleware>();
+    }
     app.UseSerilogRequestLogging();
 
     if (enableSwagger)

src/presentation/DigitalData.TaskFlow.API/appsettings.Development.json

@@ -10,6 +10,9 @@
       }
     }
   },
+  "ApiKey": {
+    "Key": null
+  },
   "Logging": {
     "LogLevel": {
       "Default": "Information",

src/presentation/DigitalData.TaskFlow.API/appsettings.json

@@ -13,6 +13,9 @@
   "ConnectionStrings": {
     "TaskFlowDb": "Server=SDD-VHP04-SQL19\\DD_TESTING01;Database=DD_ECM;User Id=sa;Password=123456789dD!;Encrypt=false;TrustServerCertificate=True;"
   },
+  "ApiKey": {
+    "Key": null
+  },
   "MediatR": {
     "LuckyPennySoftLicenseKey": "eyJhbGciOiJSUzI1NiIsImtpZCI6Ikx1Y2t5UGVubnlTb2Z0d2FyZUxpY2Vuc2VLZXkvYmJiMTNhY2I1OTkwNGQ4OWI0Y2IxYzg1ZjA4OGNjZjkiLCJ0eXAiOiJKV1QifQ.eyJpc3MiOiJodHRwczovL2x1Y2t5cGVubnlzb2Z0d2FyZS5jb20iLCJhdWQiOiJMdWNreVBlbm55U29mdHdhcmUiLCJleHAiOiIxODE2MTI4MDAwIiwiaWF0IjoiMTc4NDYyNDU1NyIsImFjY291bnRfaWQiOiIwMTk4M2M1OWU0YjM3MjhlYmZkMzEwM2MyYTQ4NmU4NSIsImN1c3RvbWVyX2lkIjoiMDE5ODNjNTllNGIzNzI4ZWJmZDMxMDNjMmE0ODZlODUiLCJzdWJfaWQiOiItIiwiZWRpdGlvbiI6IjAiLCJ0eXBlIjoiMiJ9.IUUO926m9crYGYxMjjKD_n9BnUm-EDyjFIn0YmMUCo7C-QTwvB8WhXP8veTSFsBq-leIIDJ4jyl7Pgc_7ciwg1XhUSIs4mkQroEUaSFCGOxw7Pi41WM8MK5YFSaqLTYYXec9zxgiJbGzABbh3CHTSup3okGnVm_CMoPEs91l2c0A6N1JyZy74urd_tF0KGVKf0MOvzdlQIWLQ8o73S4pTv2N-F6UlzI0fdMtTHMLNNQyr0NdWdnuBk_jMBXO-gy5RE_oCRfMTTYRX2n3XLK6pTfXE0Ct338o9F5sH8Ph2lTXSu56cpdsfZOQZGqCH0LoFp1Dd7RJgIgNmBiTGfvDnA"
   },