Version of Sitecore's CreateTicket processor for sites using CallbackAuthority setting

CustomCreateTicket.cs

using Microsoft.Owin;
using Sitecore.Abstractions;
using Sitecore.Configuration.KnownSettings;
using Sitecore.Diagnostics;
using Sitecore.Owin.Authentication.IdentityServer.Extensions;
using Sitecore.Owin.Authentication.Pipelines.CookieAuthentication.SignedIn;
using Sitecore.Owin.Authentication.Security;
using System;

namespace Identity.Pipelines.CookieAuthentication.SignedIn
{
    public class CustomCreateTicket : CreateTicket
    {
        public CustomCreateTicket(BaseTicketManager ticketManager, BaseSettings settings) : base(ticketManager, settings)
        {
        }

        public override void Process(SignedInArgs args)
        {
            Assert.ArgumentNotNull(args, nameof(args));
            if (args.AuthenticationSource != AuthenticationSource.Default || !args.Site.IsBackend && !string.Equals(args.Site.Name, "admin", StringComparison.Ordinal))
                return;

            string startUrl = args.StartUrl;
            string callbackAuthority = Settings.IdentityServer().CallbackAuthority;
            if (!string.IsNullOrEmpty(callbackAuthority) && Uri.TryCreate(callbackAuthority, UriKind.Absolute, out Uri callbackUrl))
            {
                Log.Info($"Replacing ticket URL currently: {startUrl} proxy: {callbackUrl} request: {args.Context.Request.Uri}", this);
                startUrl = startUrl.Replace(callbackUrl.GetLeftPart(UriPartial.Authority), args.Context.Request.Uri.GetLeftPart(UriPartial.Authority));
            }

            string ticket = TicketManager.CreateTicket(args.User.UserName, startUrl, true);
            if (string.IsNullOrEmpty(ticket))
                return;
            CookieOptions options = new CookieOptions()
            {
                HttpOnly = true,
                Expires = new DateTime?(DateTime.UtcNow.Add(Settings.Authentication().ClientPersistentLoginDuration))
            };
            args.Context.OwinContext.Response.Cookies.Append("sitecore_userticket", ticket, options);
        }
    }
}