Error Handling in Web Api 2

ApiExceptionResult.cs

public class ApiExceptionResult : IHttpActionResult
{
    private static readonly MediaTypeHeaderValue mediaType = new MediaTypeHeaderValue("application/json");

    private readonly ApiError errorResponse;
    private readonly JsonMediaTypeFormatter jsonMediaTypeFormatter;
    private readonly HttpRequestMessage requestMessage;
    private readonly HttpStatusCode statusCode;

    public ApiExceptionResult(HttpRequestMessage requestMessage, HttpStatusCode statusCode, ApiError errorResponse, JsonMediaTypeFormatter jsonMediaTypeFormatter)
    {
        Guard.Against.Null(requestMessage, nameof(requestMessage));
        Guard.Against.Null(statusCode, nameof(statusCode));
        Guard.Against.Null(errorResponse, nameof(errorResponse));
        Guard.Against.Null(jsonMediaTypeFormatter, nameof(jsonMediaTypeFormatter));

        this.requestMessage = requestMessage;
        this.statusCode = statusCode;
        this.errorResponse = errorResponse;
        this.jsonMediaTypeFormatter = jsonMediaTypeFormatter;
    }

    public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
    {
        var response = requestMessage.CreateResponse(statusCode, errorResponse, jsonMediaTypeFormatter, mediaType);

        return Task.FromResult(response);
    }
}

GlobalApiExceptionHandler.cs

public class GlobalApiExceptionHandler : IExceptionHandler
{
    private readonly JsonMediaTypeFormatter jsonMediaTypeFormatter;

    public GlobalApiExceptionHandler(JsonMediaTypeFormatter jsonMediaTypeFormatter)
    {
        Guard.Against.Null(jsonMediaTypeFormatter, nameof(jsonMediaTypeFormatter));

        this.jsonMediaTypeFormatter = jsonMediaTypeFormatter;
    }

    public Task HandleAsync(ExceptionHandlerContext context, CancellationToken cancellationToken)
    {
        var exception = context.Exception;

        var (code, error) = BuildError(exception);

        // Use your logging framework of choice or Kentico's EventLogProvider.LogException()
        // to log your error before sending the response

        context.Result = new ApiExceptionResult(context.Request, code, error, jsonMediaTypeFormatter);

        return Task.CompletedTask;
    }

    private (HttpStatusCode code, ApiError error) BuildError(Exception exception)
    {
        var buildApiError = CaptureErrorId(Guid.NewGuid());

        switch (exception)
        {
            case HttpException httpEx:
                return ((HttpStatusCode)httpEx.GetHttpCode(), buildApiError("HTTP_EXCEPTION", "Server error"));
            case NotAuthenticatedException notAuthNEx:
                return (HttpStatusCode.Unauthorized, buildApiError("NOT_AUTHENTICATED", "This endpoint reuires authentication"));
            case NotAuthorizedException notAuthZEx:
                return (HttpStatusCode.Forbidden, buildApiError("NOT_AUTHORIZED", "The request was not authorized to perform that action"));
            case BadRequestException badRequestEx:
                return (HttpStatusCode.BadRequest, buildApiError("BAD_REQUEST", "The request was malformed"));
            case NotFoundException notFoundEx:
                return (HttpStatusCode.NotFound, buildApiError("NOT_FOUND", "The requested data could not be found"));
            default:
                return (HttpStatusCode.InternalServerError, buildApiError("APPLICATION_EXCEPTION", "Server error"));
        }
    }

    private Func<string, string, ApiError> CaptureErrorId(Guid errorId) =>
        (string errorCode, string errorMessage) =>
        new ApiError(errorId, errorCode, errorMessage);
}

WebApiConfig.cs

public static class WebApiConfig
{
    public static HttpConfiguration ConfigureWebApi(IContainer container)
    {
        // ...

        config.Services.Replace(typeof(IExceptionHandler), container.Resolve<GlobalApiExceptionHandler>());

        // ...
    }
}