Add global exception handling middleware

Introduced `ExceptionHandlingMiddleware` to handle exceptions
globally, log errors, and return appropriate JSON responses.
Registered the middleware in `Program.cs` to ensure all requests
are processed through it. Added localization support in
`Program.cs` to enable localized error messages and other
features.

src/DigitalData.Auth.API/Middleware/ExceptionHandlingMiddleware.cs

@@ -0,0 +1,99 @@
+using DigitalData.Core.Exceptions;
+using Microsoft.AspNetCore.Mvc;
+using System.Net;
+
+namespace DigitalData.Auth.API.Middleware;
+
+/// <summary>
+/// Middleware for handling exceptions globally in the application.
+/// Captures exceptions thrown during the request pipeline execution,
+/// logs them, and returns an appropriate HTTP response with a JSON error details.
+/// </summary>
+public class ExceptionHandlingMiddleware
+{
+    private readonly RequestDelegate _next;
+    private readonly ILogger<ExceptionHandlingMiddleware> _logger;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ExceptionHandlingMiddleware"/> class.
+    /// </summary>
+    /// <param name="next">The next middleware in the request pipeline.</param>
+    /// <param name="logger">The logger instance for logging exceptions.</param>
+    public ExceptionHandlingMiddleware(RequestDelegate next, ILogger<ExceptionHandlingMiddleware> logger)
+    {
+        _next = next;
+        _logger = logger;
+    }
+
+    /// <summary>
+    /// Invokes the middleware to handle the HTTP request.
+    /// </summary>
+    /// <param name="context">The HTTP context of the current request.</param>
+    /// <returns>A task that represents the asynchronous operation.</returns>
+    public async Task InvokeAsync(HttpContext context)
+    {
+        try
+        {
+            await _next(context); // Continue down the pipeline
+        }
+        catch (Exception ex)
+        {
+            await HandleExceptionAsync(context, ex, _logger);
+        }
+    }
+
+    /// <summary>
+    /// Handles exceptions by logging them and writing an appropriate JSON response.
+    /// </summary>
+    /// <param name="context">The HTTP context of the current request.</param>
+    /// <param name="exception">The exception that occurred.</param>
+    /// <param name="logger">The logger instance for logging the exception.</param>
+    /// <returns>A task that represents the asynchronous operation.</returns>
+    private static async Task HandleExceptionAsync(HttpContext context, Exception exception, ILogger logger)
+    {
+        context.Response.ContentType = "application/json";
+
+        ValidationProblemDetails? details = null;
+
+        switch (exception)
+        {
+            case BadRequestException badRequestEx:
+                if (badRequestEx.InnerException is not null)
+                {
+                    logger.LogError(
+                        badRequestEx.InnerException,
+                        "BadRequestException inner exception captured.");
+                }
+
+                context.Response.StatusCode = (int)HttpStatusCode.BadRequest;
+                details = new() 
+                { 
+                    Title = "Bad Procedure", 
+                    Detail = badRequestEx.Message 
+                };
+                break;
+
+            case NotFoundException notFoundEx:
+                context.Response.StatusCode = (int)HttpStatusCode.NotFound;
+                details = new() 
+                {
+                    Title = "Not Found",
+                    Detail = notFoundEx.Message
+                };
+                break;
+
+            default:
+                logger.LogError(exception, "Unhandled exception occurred.");
+                context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
+                details = new()
+                {
+                    Title = "Internal Server Error",
+                    Detail = "An unexpected error occurred. Please try again later."
+                };
+                break;
+        }
+
+        if (details is not null)
+            await context.Response.WriteAsJsonAsync(details);
+    }
+}

src/DigitalData.Auth.API/Program.cs

@@ -1,6 +1,7 @@
 using DigitalData.Auth.API.Config;
 using DigitalData.Auth.API.Entities;
 using DigitalData.Auth.API.Hubs;
+using DigitalData.Auth.API.Middleware;
 using DigitalData.Auth.API.Services;
 using DigitalData.Core.Abstractions.Security.Extensions;
 using DigitalData.Core.Abstractions.Security.Services;
@@ -78,6 +79,8 @@ try
 
     var cnn_str = builder.Configuration.GetConnectionString("Default") ?? throw new InvalidOperationException("Default connection string is not found.");
 
+    builder.Services.AddLocalization();
+
     builder.Services.AddControllers();
 
     builder.Services.AddEndpointsApiExplorer();
@@ -174,6 +177,8 @@ try
 
     var app = builder.Build();
 
+    app.UseMiddleware<ExceptionHandlingMiddleware>();
+
     issuerSigningKeyInitiator = new Lazy<SecurityKey>(() =>
     {
         var factory = app.Services.GetRequiredService<IAsymmetricKeyPool>();