Hi Alpa,
Make sure you run your model reflection with ‘System’ module checked, as this is where the User entity is in which you’ll (probably) want to use.
MxModelReflection is a module from the App store that allows you to see all the objects from your domain models in the client. You need to grant a user (technical admin preferably) access to the configuration/overview page that is included in the module, where he/she can select the modules of you application that need to be synchronized, meaning: the entities of which modules need to be generated to be available in the client. Here you need to select the ‘System’ module, so it will allow you to select System.User in your SAML configuration.