Add Exception middleware

Shared/AppException.cs

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+using System.Net;
+
+namespace Diary.Shared
+{
+	public class AppException : Exception
+	{
+		public string Title { get; }
+		public HttpStatusCode StatusCode { get; }
+
+		public AppException(HttpStatusCode statusCode, string title, string message) : base(message)
+		{
+			StatusCode = statusCode;
+			Title = title;
+		}
+
+		public AppException(HttpStatusCode statusCode, string title, string message, Exception innerException) : base(message, innerException)
+		{
+			StatusCode = statusCode;
+			Title = title;
+		}
+	}
+}

Shared/ExceptionDetails.cs

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+using System.Text.Json;
+
+namespace Diary.Shared
+{
+	public class ExceptionDetails
+	{
+		public string? Message { get; set; }
+		public string? Title { get; set; }
+
+		public override string ToString()
+		{
+			var jsonSerializerSettings = new JsonSerializerOptions
+			{
+				PropertyNamingPolicy = JsonNamingPolicy.CamelCase
+			};
+
+			return JsonSerializer.Serialize(this, jsonSerializerSettings);
+		}
+	}
+
+	public class ValidationExceptionDetails : ExceptionDetails
+	{
+		public List<ValidationProblemDescriptor> ModelState { get; set; } = new();
+	}
+
+	public class ValidationProblemDescriptor
+	{
+		public string? Property { get; set; }
+		public string[]? Errors { get; set; }
+	}
+}

Shared/ExceptionHandlingMiddleware.cs

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+
+namespace Diary.Shared
+{
+	public partial class ExceptionHandlingMiddleware : IMiddleware
+	{
+		private readonly ILogger<ExceptionHandlingMiddleware> _logger;
+
+		public ExceptionHandlingMiddleware(ILogger<ExceptionHandlingMiddleware> logger)
+		{
+			_logger = logger;
+		}
+
+		public async Task InvokeAsync(HttpContext context, RequestDelegate next)
+		{
+			try
+			{
+				await next(context);
+			}
+			catch (Exception e)
+			{
+				_logger.LogError(e, "Error received from ExceptionHandlingMiddleware");
+				await HandleExceptionAsync(context, e);
+			}
+		}
+
+		private static async Task HandleExceptionAsync(HttpContext httpContext, Exception exception)
+		{
+			ExceptionDetails exceptionDetails;
+			httpContext.Response.ContentType = "application/json";
+
+			if (exception.InnerException is AppException)
+			{
+				exception = exception.InnerException;
+			}
+
+			if (exception is AppException applicationException)
+			{
+				httpContext.Response.StatusCode = (int)applicationException.StatusCode;
+
+				exceptionDetails = new()
+				{
+					Message = applicationException.Message,
+					Title = applicationException.Title
+				};
+			}
+			else
+			{
+				httpContext.Response.StatusCode = 500;
+
+				exceptionDetails = new()
+				{
+					Message = exception.Message,
+					Title = "API Error"
+				};
+			}
+
+			await httpContext.Response.WriteAsync(exceptionDetails.ToString());
+		}
+	}
+}