The System.Web.Configuration.FormsAuthenticationConfiguration can write information into the related section of the configuration file according to the restrictions defined by the section property System.Configuration.SectionInformation.AllowDefinition whose value is System.Configuration.ConfigurationAllowDefinition.MachineToApplication. Any attempt to write in a configuration file at a level not allowed in the hierarchy will result in an error message generated by the parser. However, you can use this class to read configuration information at any level in the hierarchy. For safety and scalability, it is recommended that you use an external repository, such as a database, to keep the users' credentials.