Answer - ASP.NET implements authentication using authentication providers, which are code modules that verify credentials and implement other security functionality such as cookie generation. ASP.NET supports the following three authentication providers: Forms Authentication: Using this provider causes unauthenticated requests to be redirected to a specified HTML form using client side redirection. The user can then supply logon credentials, and post the form back to the server. If the application authenticates the request (using application-specific logic), ASP.NET issues a cookie that contains the credentials or a key for reacquiring the client identity. Subsequent requests are issued with the cookie in the request headers, which means that subsequent authentications are unnecessary. Passport Authentication: This is a centralized authentication service provided by Microsoft that offers a single logon facility and membership services for participating sites. ASP.NET, in conjunction with the Microsoft® Passport software development kit (SDK), provides similar functionality as Forms Authentication to Passport users. Windows Authentication: This provider utilizes the authentication capabilities of IIS. After IIS completes its authentication, ASP.NET uses the authenticated identity's token to authorize access. To enable a specified authentication provider for an ASP.NET application, you must create an entry in the application's configuration file as follows: // web.config file