How does ASP.NET WebAPI using IIS store my users authentication state?

Question 1

I think you are misunderstanding how authentication works with ASP.Net. As an example, let me show you some cookie details for a site of mine that uses Identity (note the token is actually in the cookie, the two are not mutually exclusive concepts):

Name    __RequestVerificationToken
Value   afeILhaIvRr56jXXXXXXXXXXX
Host    site.azurewebsites.net
Path    /
Expires At end of session

Note that the cookie, by default, expires at the end of your session. That means when you restart your development machine, your cookie is expired and your token is no longer valid.

In particular I have read that with token authentication then there is no need for continual re-authentication every time a request is made to the server

You need to understand that HTTP is a stateless protocol. Each request happens in a vacuum, and therefore you need to pass some data back to the server so that it can tell that the person who authenticated with Request A is really the initiator of Request B. Almost always, that piece of data is from a cookie. So, every request does indeed re-authenticate, and typically with a token in a cookie.

The only piece of data about your session that is stored on the client is the cookie (unless you are doing something atypical). The rest is on the server. How it is stored can vary:

Inproc: Easiest to setup, sessions are stored in process. So when your server or app pool is restarted, that data disappears

State Server Mode: Sessions are stored in process, but outside of the ASP.Net worker process, so the application can be restarted without losing session data

SQL Server: Unsurprisingly, this stores data in a database. Very resilient, but more work to setup. Also your best option if you are on a web farm.

ref: http://msdn.microsoft.com/en-us/library/vstudio/ms178586(v=vs.100).aspx

Question 2

Expanding on the great answer by Chris, I would like to add that there are two possible models here. In forms authentication (which is the default membership type for asp.net) the cookie can either store authentication information and then it's called a ticket or the information can be stored in session, with the cookie being a simple identifier for "reconnecting" the authenticated session with the requesting client on each subsequent request.

This "reconnecting" happens in the Application_AuthenticateRequest method of the global.asax. If you are using the default forms authentication storage, i.e. an SQL DB created for you by the framework, the reconnection will be done automatically. If you are using a custom authentication store (like accessing active directory yourself or a custom users table structure) you can override the the method and reconnect the authenticated session using your own implementation. In any case, the authentication data is populated in the User.Identity object's different properties. From that point, if you use the [Authorize] attribute, the framework accesses the object to check if the user is indeed authenticated and authorized.

I any case, the authentication information is tied to both the cookie and the session. Assuming your session is InProc, like Chris said, when the session is lost (through timeout, app pool recycle or restart of the dev machine) the server-side of the session is lost and your authentication / session cookie is replaced by a new one on the next request.

EDIT: Ohh... and one more side comment. Make sure you distinguish between authentication and authorization. The client is not re-authenticated on each request. Authentication is the process of providing your credentials and being identified by the server. Authorization is, now that the server has verified who you are, on each request it checks if you are authorized to access the resource you are requesting.

Question 3

The server doesn't store information about who's authenticated and who isn't. Depending on your authentication mechanism (forms, tokens?), typically, when a user logs in, the server will return some form of authentication token that the client should pass back to the server on each API call.

Without knowing more about your configuration, it's difficult to explain why when you restart your server you have to re-authenticate, it sounds like the authentication token generated by the server is invalidated on restart.

Question 4

Where and how does the Server or IIS store information on which users have authenticated?

IIS does not store state based on cookie authentication. Everything is determined based on the request. Either a request has the correct encrypted information, or it doesn't. If you look at a default Forms authentication in ASP.NET, you will find a cookie called .ADUAUTH ... this cookie has all the information to authenticate the request. If the cookie is half expired, it will be reset, but that's all IIS does.

Does it do this just the once or on every HTTP?

Every HTTP request is unique, so yes, per HTTP request.

Is there a difference between my using Token or cookie authentication in the way that the authentication and also authorization is checked on the server?

It's always checked on the server: To find out more, check out: How ASP.NET Security Works: http://msdn.microsoft.com/en-us/library/ks310b8y.ASPX

Question 5

I think my answer could be a little contradicting to all of the above.. But I think If I understand right..

IIS stores inside the memory space of the ASP.NET worker process, i.e the session data in the RAM.

The storing of authentication state depends on the authentication model you are using. For example: if you are using the Federated authentication, through ADFS, then when a user loads your web page he is required to sign in providing his credentials. The ADFS then sets the authentication token which is stored in the session data, the session id is stored as cookies in user's browser. The server has the mapping of Session Id to its session data.

Now the user is authenticated. The ADFS looks for authentication token to mark a user as authenticated.

When you restart the server, the session data is lost as the data is stored in RAM.

There are ways to handle this, there are 3 types of session storage: 1. InProc (Stored in memory space of ASP .NET Worker process - RAM) 2. State Server (Stored out side of ASP .NET worker process, like on cloud Azure storage) 3. SQL Server session storage (Stored in SQL server)

I think you are adopting 1, because of which you encounter the problem. In cases 2 and 3, the session is not lost when you restart the server.

Question 6

Several things --

Token based authentication is not really authentication. It is just issuing you a unique token (can be a guid, unique string, etc) and then associating it with something (like your IP address) and saving that association server side (in a database?). Now whenever you use that token, from the client app, the server checks the association already stored and serves or denies or request.

In many ways, it is very similar to using Cookies to maintain authentication. Only, token-auth was designed more for web services operation than for UIs.

Question 7

In short: Out of the box, the membership provider will run it's authentication method and upon success, it will create an auth ticket/token/cookie that will be stored from the site. In addition to this, there is a session cookie that is stored with the site as well. When you make a page request, it'll pull these things and use them to determine whether or not you are already authenticated. If it finds the ticket and sees that it is still good, it'll allow access.

When you restart your local environment, the session and it's information is destroyed which is why you have to log in again.

There is an entire pipeline in the framework that makes all of this stuff happen (having to do with authentication, authorization, and identity) and there are number of ok articles on the interwebs explaining this, but imo, they're almost all incomplete or hard to follow. If you want a great soup-to-nuts explanation, PluralSight.com has some training videos that will deconstruct and explain the entire pipeline for you. Understanding the pipeline can help you implement your own custom authentication, and I highly recommend it.