After you’ve created a user role of type ‘Guest User’ you can add a sign-in microflow at “Project security”. You have to set the security level to Prototype / demo or Production. The tab “Anonymous users” will appear. Within this tab you’re able to select a sign in microflow. You’re custom sign-in microflow should contain 2 parameters: 1.) AnonymousUser and 2.) SignedInUser (case sensitive). After that, you can model your own login logic and combine this with opening a start page.