The error : "The type of page you have requested is not served because it has been explicitly forbidden." is thrown because the user you use does not have permissions to see requested page. If a user does not belong to any role he/she does not have rights to view, edit, modify etc. pages and content.
When Allow Anonymous is set to true - all users can see this page although they might have not been authenticated. When Allow Anonymous is set to false - only authenticated users - that have supplied their credentials have access to a given resources.
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