Refresh scan options stopped working

I am using the following code inside a section Application_Start

. This updates the web.config with the latest token and is used in all tutorials for applications that use Azure AD.

My application, which is running successfully, now failed to start with an Access Denied error on the web.config path associated with this code. The code itself hasn't changed, so I'm assuming there is some kind of security update. I cannot find a link to the bug or update on the internet. The security settings in the folder look just fine. Redistribution does not permit this.

protected void RefreshValidationSettings()
{
     string configPath = AppDomain.CurrentDomain.BaseDirectory + "\\" + "Web.config";
     string metadataAddress = 
         ConfigurationManager.AppSettings["ida:FederationMetadataLocation"];
     ValidatingIssuerNameRegistry.WriteToConfig(metadataAddress, configPath);
}