Getting Access Denied error while checking out Master Page Gallery using pnp C# code

[vvenkataratnam]

We had C# code to provision a new site using PnP C# library with XMLTemplateProvider, that used to work from past 6+ years. Recently, we are facing the following error while trying to check out the Master Page Gallery.

Error: Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))

Appreciate, if someone could share why we are getting this error and what has changed recently in SharePoint?

using (var repositoryContext = new AuthenticationManager().GetAppOnlyAuthenticatedContext(templatesSiteUrl,clientId,clientSecret))  {
    var mpgallery = web.GetListByTitle("Master Page Gallery");   
    mpgallery.ForceCheckout = true;   
    mpgallery.Update();   
    web.Context.ExecuteQueryRetry();
}

[pkbullock]

Hi, you will need to provide an alternative service principal since the app PnP Management Shell has been removed: https://pnp.github.io/powershell/articles/registerapplication.html

[vvenkataratnam]

Hi Paul,
Thanks for the reply. After Setting up access using our own Entra ID App for App Only Access, can we use pnp framework in C# and perform force checkout on master page gallery?

[jansenbe]

If you grant it the needed permissions then yes

[vvenkataratnam]

I have created the new app registration in Azure and set it up for App Only Access and using the following powershell script to check out the master page gallery.

Connect-PnPOnline -ClientId $ClientID -CertificatePath $CertificationPath -CertificatePassword (ConvertTo-SecureString -AsPlainText "XYZ" -Force) -Url $SiteURL -Tenant $Tenant
Get-PnPList

# Set the Master Page Gallery (/_catalogs/masterpage) to require checkout
Set-PnPList -Identity "Master Page Gallery" -ForceCheckout $true

I am able to see the lists, but still getting Access Denied, when trying to use Set-PnPList

What are the other permissions, I need to set, so that I can use Set-PnPList