https://www.youtube.com/watch?v=4LaFi0SzBdY

Thank you!!! My [ValidateAntiForgeryToken] errors are still not well-handled this way, but I will try again..
I see that it does not even route to "/error"..

like I said, validateantiforgery does not have anything to do with authentication. The antiforgery prevents csrf attacks.

Finally I did not use your video, I used something else:

I created a new class: "RedirectAntiforgeryValidationFailedResultFilter".

This class inherits: IAsyncAlwaysRunResultFilter

The class looks like this:

using Umbraco.Cms.Web.Website.ActionResults;  
using UMmebers10.ViewComponentClasses;
using Umbraco.Cms.Infrastructure.Examine;

namespace UMmebers10.Classes
{
    public class RedirectAntiforgeryValidationFailedResultFilter : IAsyncAlwaysRunResultFilter<br/>
    {
        public Task OnResultExecutionAsync(ResultExecutingContext context, ResultExecutionDelegate next)
        {
            if (context.Result is AntiforgeryValidationFailedResult)
            {
                context.Result = new RedirectToPageResult("/ErrorPage");
            }
            return next();
        }
    }

This works!!!!

But the problem that I have is about the line:

context.Result = new RedirectToPageResult("/ErrorPage");

I am redirected to a non existing page:

https://localhost:44358/umbraco/backoffice/api/filestree/HandleDeposit?page=%2FErrorPage

I want to be redirected to an existing page like:

context.Result = new RedirectToPageResult(MasterPage.Url);

But I dont know how "MasterPage" should be defined.

Mainly because: "Umbraco.AssignedContentItem" or "CurrentPage" are not defind in a class that does not inherit from "SurfaceController".

Can you please help? Thank you!!!

Finally it worked using this code (Adding new class):

using Umbraco.Cms.Web.Website.ActionResults;
using UMmebers10.ViewComponentClasses;
using Umbraco.Cms.Infrastructure.Examine;

namespace UMmebers10.Classes
{
    public class RedirectAntiforgeryValidationFailedResultFilter : IAsyncAlwaysRunResultFilter
    {
        public Task OnResultExecutionAsync(ResultExecutingContext context, ResultExecutionDelegate next)
        {
            if (context.Result is AntiforgeryValidationFailedResult)
            {
                context.Result = new RedirectToPageResult("/ErrorPage");
            }

            return next();
        }
    }
}

And, in startup.cs code:

services.AddMvc(options =>
    options.Filters.Add<RedirectAntiforgeryValidationFailedResultFilter>())
    .SetCompatibilityVersion(CompatibilityVersion.Version_2_2)
    .ConfigureApiBehaviorOptions(options =>
    {
        options.SuppressMapClientErrors = true;
    });

The only problem left: I am redirected to a non-existing page:

https://localhost:44358/umbraco/backoffice/api/filestree/HandleDeposit?page=%2FErrorPage

How can I find the home page root and redirect there?

The class does not inherit SurfaceController, so Codes like "CurrentPage" and "Umbraco.AssignedContentItem" are not recognized there, and I don't know how they can be recognized,