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ASP.NET Forms Authentication Overview

Forms authentication lets you authenticate users by using your own code and then maintain an authentication token in a cookie or in the page URL. Forms authentication participates in the ASP.NET page life cycle through the FormsAuthenticationModule class. You can access forms authentication information and capabilities through the FormsAuthentication class.

To use forms authentication, you create a login page that collects credentials from the user and that includes code to authenticate the credentials. Typically you configure the application to redirect requests to the login page when users try to access a protected resource, such as a page that requires authentication. If the user's credentials are valid, you can call methods of the FormsAuthentication class to redirect the request back to the originally requested resource with an appropriate authentication ticket (cookie). If you do not want the redirection, you can just get the forms authentication cookie or set it. On subsequent requests, the user's browser passes the authentication cookie with the request, which then bypasses the login page.

You configure forms authentication by using the authentication configuration element. In the simplest case, you have a login page. In the configuration file, you specify a URL to redirect unauthenticated requests to the login page. You then define valid credentials, either in the Web.config file or in a separate file. The following example shows a section from a configuration file that specifies a login page and authentication credentials for the Authenticate method. The passwords have been encrypted by using the HashPasswordForStoringInConfigFile method.

<authentication mode="Forms">
   <forms name="SavingsPlan" loginUrl="/Login.aspx">
      <credentials passwordFormat="SHA1">
         <user name="Kim"
               password="07B7F3EE06F278DB966BE960E7CBBD103DF30CA6"/>
         <user name="John"
               password="BA56E5E0366D003E98EA1C7F04ABF8FCB3753889"/>
      </credentials>
   </forms>
</authentication>

After successful authentication, the FormsAuthenticationModule module sets the value of the User property to a reference to the authenticated user. The following code example shows how to programmatically read the identity of the forms-authenticated user.

String authUser2 = User.Identity.Name;

A convenient way to work with forms authentication is to use ASP.NET membership and ASP.NET login controls. ASP.NET membership lets you store and manage user information and includes methods to authenticate users. ASP.NET login controls work with ASP.NET membership. They encapsulate the logic to prompt users for credentials, validate users, recover or replace passwords, and so on. In effect, ASP.NET membership and ASP.NET login controls provide a layer of abstraction over forms authentication. These features replace most or all the work that you would ordinarily have to do to use forms authentication. For more information, see Managing Users by Using Membership and the ASP.NET Login Controls Overview.

You can also access forms authentication as a Windows Communication Framework (WCF) service by using the ASP.NET authentication service. The authentication service enables you to use forms authentication from any application that can send and consume messages in SOAP format. The authentication service accepts user credentials and returns a forms authentication cookie.

For example, you can log in users from an application that was not developed with the .NET Framework. For more information, see Windows Communication Foundation Authentication Service Overview.

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