Authentication in ASP.NET

Authentication in ASP.NET

There are two closely interlinked concepts at the heart of security for distributed applications - authentication and authorization. Authentication is the process of obtaining some sort of credentials from the users and using those credentials to verify the user's identity. Authorization is the process of allowing an authenticated user access to resources. Authentication is always precedes to Authorization; even if your application lets anonymous users connect and use the application, it still authenticates them as being anonymous.
ASP.net provides flexible set of alternatives for authentication. You can perform authentication yourself in code or delegate authentication to other authorities (such as Microsoft Passport). In fact sometimes it seems ASP.net authentication is a bit too flexible; it can be difficult for a new developer to know just where to start. In this article, we review the settings in ASP.net and Internet Information Services (IIS) that control authentication and authorization in ASP.net applications.

An ASP.net application has two separate authentication layers. That is because ASP.net is not a standalone product. Rather it is a layer on top of IIS. All requests flow through IIS before they are handed to ASP.net. As a result, IIS can decide to deny access without the ASP.net process even knowing that someone requested a particular page. Here is an overview of the steps in the joint IIS and ASP.net authentication process.

1. IIS first checks to make sure the incoming request comes from an IP address that is allowed access to the domain. If not it denies the request.
2. Next IIS performs its own user authentication if it configured to do so. By default IIS allows anonymous access, so requests are automatically authenticated, but you can change this default on a per - application basis with in IIS.
3. If the request is passed to ASP.net with an authenticated user, ASP.net checks to see whether impersonation is enabled. If impersonation is enabled, ASP.net acts as though it were the authenticated user. If not ASP.net acts with its own configured account.
4. Finally the identity from step 3 is used to request resources from the operating system. If ASP.net authentication can obtain all the necessary resources it grants the users request otherwise it is denied. Resources can include much more than just the ASP.net page itself you can also use .Net's code access security features to extend this authorization step to disk files, Registry keys and other resources.