Just upgraded our portal to 10.7 and now cannot connect from Runtime application

Receive the following error:

The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.

 

The remote certificate is invalid according to the validation procedure.

This same code worked at 10.6.1 (and has worked on previous versions).  If I change to using agol it will work

public async Task<TokenCredential> GetPortalCredential(string user, string password)
{
     try
     {
          var portalUri = new Uri($"{ConfigurationSettings.PortalUrl}/sharing/rest");
          var credential = await AuthenticationManager.Current.GenerateCredentialAsync(portalUri, user, password);
          return credential;
     }
     catch (Exception e)
     {
          _log.Log(e.Message, Category.Exception, Priority.None);

          return null;
     }
}