Emad's Blog

In order to grant authenticated FBA users access to a custom application page (/_layouts page), please follow these steps:

• The Page should inherit from LayoutsPageBase (Making it inherit from UnsecuredLayoutsPageBase will grant anonymous access to this page).
• Override the Properties RightsRequired and RequireDefaultLayoutsRights

       protected override SPBasePermissions RightsRequired
       {
           get
           {
               SPBasePermissions permissionRequired = SPBasePermissions.ViewPages;
               return permissionRequired;
           }
       }

       protected override bool RequireDefaultLayoutsRights
       {
           get
           {
               return false;
           }
       }

This will grant authenticated FBA users access to this _Layouts page.