SF_11.0, SF_11.1, SF_11.2, SF_12.0, SF_12.1, SF_12.2, SF_13.0, SF_13.1, SF_13.2, SF_13.3, SF_14.0, SF_14.1, SF_14.2, SF_14.3 - https://www.progress.com/documentation/sitefinity-cms/administration-configure-ssl

ConfigureFrontendPagesRequireSSL.cs

using System.Linq;
using Telerik.Sitefinity.Abstractions;
using Telerik.Sitefinity.Modules.Pages;
using Telerik.Sitefinity.Pages.Model;

namespace SitefinityWebApp
{
    public class ConfigureFrontendPagesRequireSSL
    {
        public void EnableRequireSSL()
        {
            PageManager pageManager = PageManager.GetManager();
            IQueryable<PageNode> pageNodes = pageManager.GetPageNodes().Where(pn => pn.RootNodeId == SiteInitializer.CurrentFrontendRootNodeId);

            foreach (var pageNode in pageNodes)
            {
                pageNode.RequireSsl = true;
            }
            pageManager.SaveChanges();
        }
    }
}