The time you start developing your web application until you finish the application, you will more often use the Web.config file not only for securing your application but also for wide range of other purposes which it is intended for. ASP.NET Web.config file provides you a flexible way to handle all your requirements at the application level. Despite the simplicity provided by the .NET Framework to work with web.config, working with configuration files would definitely be a task until you understand it clearly. This could be one of the main reasons that I started writing this article.
Web.config File – ASP.NET – CodeProject