This provider utilizes the authentication capabilities of IIS. After IIS completes its authentication, ASP.NET uses the authenticated identity's token to authorize access. This type of authentication is possibly the easiest of all to implement. Windows authentication can be used in conjunction with almost all authentication methods provided by IIS, except Anonymous Authentication. There is no need to write any code to validate the user as IIS has already authenticated their Windows credentials. Basically, Windows authentication makes use of the authentication capabilities of IIS. IIS will complete its authentication first then ASP.NET will use the authenticated identity's token to decide whether the access is granted or denied.

This mechanism is usually implemented when the users are part of Windows domain and the authenticated users are to be impersonated so that the code is executed in the same security context of the user's Windows account.

When a user requests specific resources, this request will go to IIS. IIS authenticates the user and attaches the security token to it. It will then pass the authenticated request and security token to ASP.NET. If impersonation is enabled, ASP.NET impersonates the user using the security token attached and sees whether the user is authorized to access the resources in the <authorization> section in Web.config file. If the access is granted, ASP.NET will send the requested resources through IIS, or else, it sends error message to the user.

There are four different kinds of Windows authentication options available that can be configured in IIS:

• Anonymous Authentication:
IIS doesn't perform any authentication check. IIS allows any user to access the ASP .NET application.

• Basic Authentication:
For this kind of authentication, a Windows user name and password has to be provided to connect.

• Digest Authentication:
It is same as Basic Authentication but for the fact that the password is hashed before it is sent across the network. However, to be using Digest Authentication, we must use IE 5.0 or above.