An Overview of Forms Authentication (C#)

https://docs.microsoft.com/en-us/aspnet/web-forms/overview/older-versions-security/introduction/an-overview-of-forms-authentication-cs

Introduction

In the preceding tutorial we discussed the various authentication, authorization, and user account options provided by ASP.NET. In this tutorial we will turn from mere discussion to implementation; in particular, we will look at implementing forms authentication. The web application we start constructing in this tutorial will continue to be built upon in subsequent tutorials, as we move from simple forms authentication to membership and roles.

This tutorial begins with an in-depth look at the forms authentication workflow, a topic we touched upon in the previous tutorial. Following that, we will create an ASP.NET website through which to demo the concepts of forms authentication. Next, we will configure the site to use forms authentication, create a simple login page, and see how to determine, in code, whether a user is authenticated and, if so, the username they logged in with.

Understanding the forms authentication workflow, enabling it in a web application, and creating the login and logoff pages are all vital steps in building an ASP.NET application that supports user accounts and authenticates users through a web page. Because of this – and because these tutorials build upon one another - I would encourage you to work through this tutorial in full before moving on to the next one even if you already have had experience configuring forms authentication in past projects.