Getting error "The app principal does not exist" when connecting to SharePoint Online from a C# Console App

Question

Having recently moved our intranet from SharePoint on-premises to SharePoint Online, I'm now trying to get a bunch of C# Console Apps (.NET Framework) to work with the new version of the sites. I believe I can use the PnP Framework to do this but I'm struggling to connect to SharePoint Online successfully. I've set up an App Registration in Azure and I'm using the ClientID and ClientSecret in my code, which is as follows:

using Microsoft.SharePoint.Client;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using PnP.Framework;

namespace SPOTest3_pnp
{
    internal class Program
    {
        static void Main(string[] args)
        {
            string siteUrl = @"https://mycompany.sharepoint.com/sites/mysite"; 
            string clientId = "12345678-1234-1234-1234-123456789012"; 
            string clientSecret = "1234567890123456789012345678901234567890"; 
            using (var clientContext = new AuthenticationManager().GetACSAppOnlyContext(siteUrl, clientId, clientSecret))
            {
                clientContext.Load(clientContext.Web, p => p.Title);
                clientContext.ExecuteQuery();
                Console.WriteLine(clientContext.Web.Title);
            };
        }
    }
}

The call to ExecuteQuery() however return this error:

Microsoft.SharePoint.Client.ClientRequestException: 'Cannot contact site at the specified URL https://mycompany.sharepoint.com/sites/mysite. The app principal does not exist.'

I can't find anything useful to explain what that error refers to in this case or how to fix it. Any help would be gratefully received.

Answer 1

The error suggests that register add-in is missing in SharePoint site. Please follow below steps to register the add-in in SharePoint site.

Register Add-In using the AppRegNew form

• Navigate to [Site Collection URL]/_layouts/15/AppRegNew.aspx
• At this point, you’ll need to fill in the following details
• Once you have filled in all the details, hit Create to register the add-in.
• You will be navigated to a page displaying the details of your add-in. Save Client Id & Client Secret for future references.

Grant permission to an add-in

Now that the identifier is created, we need to grant the necessary permission for it to perform any action. In this example, I’ll demonstrate how to grant full control access on a Site Collection.

• Navigate to [Site Collection URL]/_layouts/15/AppInv.aspx

• Enter your Client Id value in the App Id option and hit the Lookup button. Details of your add-in will be displayed automatically.

• This is the crucial part. In the option, Permission Request XML, let’s write the below XML code to grant our add-in full control on the given site collection.

• Just hit the Create button. You will now be prompted to trust the add-in for all the permissions that it requires.

• Hit the Trust It to grant the requested accesses. You can navigate to the following URL to also confirm that the permission has been assigned to the add-in. [Site Collection URL]/_layouts/15/appprincipals.aspx

Reference link: https://piyushksingh.com/2018/12/26/register-app-in-sharepoint/