C# code to add/remove/list globally-deployed SPFx extensions (with skipFeatureDeployment=true), specifically Application Customizers, using OfficeDevPnP.Core

ManageSPFxExtension_Methods.cs

using Microsoft.SharePoint.Client;
using OfficeDevPnP.Core;
using OfficeDevPnP.Core.Entities;
using System;
using System.Linq;

namespace COB.SPFx.Extensions.Manage
{
    /// <summary>
    /// Console app code to add/remove/list SPFx Application Customizer extensions..
    /// </summary>
    class Program
    {
        // TODO: provide details of a single site here, or provide some code to iterate several sites..
        private static readonly string SITE_URL = "TODO";
        private static readonly string USERNAME = "TODO";
        private static readonly string PWD = "TODO";

        static void Main(string[] args)
        {
            AuthenticationManager authMgr = new AuthenticationManager();
            ClientContext ctx = authMgr.GetSharePointOnlineAuthenticatedContextTenant(SITE_URL, USERNAME, PWD);
            Web currentWeb = ctx.Web;
            ctx.Load(currentWeb);
            ctx.ExecuteQueryRetry();

            Console.WriteLine(string.Format("Main: Authenticated to site - '{0}'.", ctx.Web.Url));

            // TODO: comment in/out method calls here as you need..
            getCustomActions(ctx);
            //addSpfxExtensionCustomAction(ctx);
            //removeSpfxExtensionCustomAction(ctx, "COB-SPFx-GlobalHeader");
            
            Console.ReadLine();
        }


        private static void addSpfxExtensionCustomAction(ClientContext ctx)
        {
            Console.WriteLine(string.Format("addSpfxExtensionCustomAction: Adding extension to web - '{0}'.", ctx.Web.Url));

            Guid spfxExtension_GlobalHeaderID = new Guid("4a79203e-287d-4173-82c9-0111232c6c2e");
            string spfxExtName = "COB-SPFx-GlobalHeader";
            string spfxExtTitle = "COB-SPFx-GlobalHeader";
            string spfxExtGroup = "";
            string spfxExtDescription = "Adds a global header/footer to the site";
            string spfxExtLocation = "ClientSideExtension.ApplicationCustomizer";

            CustomActionEntity ca = new CustomActionEntity
            {
                Name = spfxExtName,
                Title = spfxExtTitle,
                Group = spfxExtGroup,
                Description = spfxExtDescription,
                Location = spfxExtLocation,
                ClientSideComponentId = spfxExtension_GlobalHeaderID
            };

            ctx.Web.AddCustomAction(ca);
            ctx.ExecuteQueryRetry();

            Console.WriteLine(string.Format("addSpfxExtensionCustomAction: Successfully added extension to web - '{0}'.", ctx.Web.Url));

            Console.WriteLine(string.Format("addSpfxExtensionCustomAction: Leaving."));
        }

        private static void removeSpfxExtensionCustomAction(ClientContext ctx, string extensionName)
        {
            Console.WriteLine(string.Format("removeSpfxExtensionCustomAction: Removing extension with name '{0}' from web - '{1}'.",
                extensionName, ctx.Web.Url));

            var customActionsToRemove = ctx.Web.GetCustomActions().Where(ca => 
                ca.Location == "ClientSideExtension.ApplicationCustomizer" && 
                ca.Name == extensionName);

            if (customActionsToRemove.Count() > 0)
            {
                foreach (var ca in customActionsToRemove)
                {
                    ctx.Web.DeleteCustomAction(ca.Id);
                    ctx.Web.Update();
                    ctx.ExecuteQueryRetry();

                    Console.WriteLine(string.Format("removeSpfxExtensionCustomAction: Successfully removed extension '{0}' from web '{1}'.",
                        extensionName, ctx.Web.Url));
                }
            }
            else
            {
                Console.WriteLine(string.Format("removeSpfxExtensionCustomAction: Did not find any extension to remove named '{0}' on web '{1}'.",
                        extensionName, ctx.Web.Url));
            }

            Console.WriteLine("removeSpfxExtensionCustomAction: Leaving.");
        }

        private static void getCustomActions(ClientContext ctx)
        {
            Console.WriteLine(string.Format("getCustomActions: Retrieving extensions for web - '{0}'.", ctx.Web.Url));

            var customActions = ctx.Web.GetCustomActions().Where(ca => ca.Location == "ClientSideExtension.ApplicationCustomizer");
            if (customActions.Count() > 0)
            {
                foreach (var ca in customActions)
                {
                    Console.WriteLine(string.Format("getCustomActions: Found extension with name - '{0}', ClientSideComponentId ='{1}'.",
                        ca.Name, ca.ClientSideComponentId));
                }
            }
            else
            {
                Console.WriteLine("getCustomActions: No extensions found.");
            }

            Console.WriteLine("getCustomActions: Leaving.");
        }
    }
}