Owin is the next hot thing that everyone (or at least those following the bleeding edge of .NET development) is talking about. When creating a new ASP.NET project it references Owin for the ASP.NET Identity authentication system so it’s obviously not only a hype but actively used. But what is it really and why should I care?

What is this Owin thing?

TL;DR;

Owin is the under the hood interface between web servers and web applications. If you only write web applications in a single framework (such as ASP.NET MVC) an only run on one server platform (Windows with IIS) you can ignore Owin. But it will change the development and deployment landscape for ASP.NET so total ignorance can be risky.

The Complete Story

Owin is a new standardised interface between web servers and web applications. It is meant as a away to break up the tight coupling between ASP.NET and IIS. With IIS supporting Owin it is possible to run other Owin-enabled frameworks such as Nancy on IIS. With Microsoft’s web frameworks depending on Owin and not IIS it is possible to run those in other environments, such as self hosting within a process or on a web server on linux running Mono. SignalR and Web API already uses Owin which means that they can be self hosted and other cool stuff. ASP.NET MVC6 which is part of ASP.NET vNext will be completely based on Owin.

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ASP.NET Identity is the reworked, flexible replacement for the old membership system that has been around since ASP.NET 2.0. ASP.NET Identity is more well designed and flexible than the old membership system and uses Owin middleware components for external logins such as Facebook, Google and Twitter.

Compared to the membership system, the architecture of ASP.NET Identity is very much improved and decoupled. Actually, ASP.NET identity doesn’t know (nearly) anything about Owin at all. ASP.NET Identity is working on an application ignorant level, taking care of user and role storage. Then there are the Owin authentication modules that takes care of the actual interaction with the external providers and keeping the user session. The plumping code required is built into the AccountController created by the new project wizard for ASP.NET projects.

Typical Layering

For a typical application there will be a number of different application layers cooperating to provide the authentication functionality.

• The ASP.NET Identity module sits at the very bottom of the chain, far, far away from the incoming HTTP Request. In fact, it knows nothing about Http at all.
• The MVC AccountController provides all the plumbing to make the different modules interact with each other.
• The Google Authentication Middleware interacts with Google to provide Google signon. In this example I only show Google, but if more social networks such as Facebook or Twitter were offered, they would be next to the Google middleware in the stack.
• The MVC Acount Controller is the generated MVC controller that ties all of the layers together.
• The ASP.NET Identity module handles user and secure password storage, role mapping etc.

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Owin makes it easy to inject new middleware into the processing pipeline. This can be leveraged to inject breakpoints in the pipeline, to inspect the state of the Owin context during authentication.

When creating a new MVC 5.1 project a Startup.Auth.cs file is added to the project that configures the Owin pipeline with authentication middleware. Two middleware for authentication are enabled through calls to app.UseCookieAuthentication() and app.UseExternalSignInCookie. There are also commented out sections for Microsoft, Twitter, Facebook and Google authentication. This post will use Google Authentication as an example and also add some “dummy” middleware that makes it possible to set breakpoints and inspect the authentication pipeline.

Inserting Breakpoint Middleware

The middleware is executed in the order they are listed in the file, so by inserting a simple middleware between the existing, it is possible to inspect how each middleware interact with the authentication pipeline.

The injected middleware is just a few lines of code, but it allows two breakpoints to be set: on the opening and closing braces, which enables inspection before and after the call to the next middleware.

app.Use(async (context, next) =>
{
  await next.Invoke();
});

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Owin and Katana offers a flexible pipeline for external authentication with existing providers for authentication by Google, Facebook, Twitter and more. It is also possible to write your own custom authentication provider and get full integration with the Owin external authentication pipeline and ASP.NET Identity.

Anatomy of an Owin Authentication Middleware

For this post I’ve created a dummy authentication middleware that interacts properly with the authentication pipeline, but always returns the same user name. From now on I will use the names from that dummy for the different classes.

A typical Katana middleware is made up of 5 classes.

1. The main DummyAuthenticationMiddleware class.
2. The internal DummyAuthenticationHandler class doing the actual work.
3. A DummyAuthenticationOptions class for handling settings.
4. An extension method in DummyAuthenticationExtensions for easy setup of the middleware by the client application.
5. An simple internal Constants class holding constants for the middleware.

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ASP.NET MVC5 has excellent support for external social login providers (Google, Facebook, Twitter) integrating with the ASP.NET Identity system. But what if we want to use external logins directly without going through ASP.NET Identity? Using external logins together with ASP.NET Identity is very simple to get started with, but it requires all users to register with the application. External logins are just another authentication method against the internal ASP.NET Identity user. In some cases there is no need for that internal database, it would be better to get rid of it and use the external login providers without ASP.NET Identity. That’s possible, but requires a bit of manual coding.

For public facing web applications I think that it is often a good idea to use ASP.NET Identity as it doesn’t tie the user to a specific login provider. But if we are fine with using one and only one specific login provider for each user it’s possible to skip ASP.NET Identity. It could be an organization that heavily relies on Google Apps already so that all users are known to have Google accounts. It could be an application that uses SAML2 based federative login through Kentor.AuthServices.

In this post I’ll start with a freshly created ASP.NET MVC Application without any authentication at all and make it use Google authentication, without ASP.NET Identity being involved at all. The complete code is available on my GitHub account.

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