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How to Implement SSO with OWIN and ASP.NET Identity

By: Author Alex Lim

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Learn how to implement single sign-on (SSO) with OWIN and ASP.NET Identity for two web apps using OAuth bearer tokens and Angular.

Single sign-on (SSO) is a user authentication method that allows a user to access multiple web applications with one set of login credentials. SSO improves the user experience, reduces the risk of password fatigue, and enhances security. In this article, you will learn how to implement SSO with OWIN and ASP.NET Identity for two web apps using OAuth bearer tokens and Angular. You will also learn how to create a custom SSO provider without using any third-party services.

What is OWIN?

OWIN stands for Open Web Interface for .NET. It is a specification that defines a standard interface between .NET web servers and web applications. OWIN decouples the web application from the server, making it easier to host, test, and scale web applications. OWIN also provides a middleware pipeline that can handle various tasks such as authentication, logging, routing, etc.

What is ASP.NET Identity?

ASP.NET Identity is a membership system that allows you to add user authentication and authorization to your web applications. ASP.NET Identity supports various authentication methods, such as username and password, social login, two-factor authentication, etc. ASP.NET Identity also provides a flexible and extensible framework for managing user data, roles, claims, and external providers.

What is OAuth?

OAuth is an open standard for authorization that allows a third-party application to obtain limited access to a protected resource on behalf of a user. OAuth uses an access token that is issued by an authorization server after the user grants permission to the client application. The client application can then use the access token to access the protected resource on the resource server.

How to Implement SSO with OWIN and ASP.NET Identity?

To implement SSO with OWIN and ASP.NET Identity, you need to do the following steps:

  1. Create two web applications that use OWIN and ASP.NET Identity. You can use the ASP.NET Web Application template and select the Web API option. You also need to install the following NuGet packages:
    • Microsoft.AspNet.Identity.Owin
    • Microsoft.Owin.Host.SystemWeb
    • Microsoft.Owin.Security.OAuth
  2. Configure the OAuth authorization server and the OAuth bearer authentication middleware in the Startup class of each web application. The OAuth authorization server is responsible for generating and validating the access tokens. The OAuth bearer authentication middleware is responsible for authenticating the access tokens and setting the user identity. You can use the OAuthAuthorizationServerOptions and OAuthBearerAuthenticationOptions classes to configure the options for the OAuth components. For example, you can set the AuthorizeEndpointPath, TokenEndpointPath, AccessTokenExpireTimeSpan, Provider, etc. for the OAuth authorization server, and the Provider, AuthenticationMode, etc. for the OAuth bearer authentication middleware.
  3. Implement the logic for the OAuth authorization server provider in a class that inherits from OAuthAuthorizationServerProvider. This class handles the requests to the authorization endpoint and the token endpoint. You need to override the following methods:
    • ValidateClientAuthentication: This method validates the client credentials and sets the client identity.
    • GrantResourceOwnerCredentials: This method validates the user credentials and sets the user identity and claims.
    • TokenEndpoint: This method adds additional data to the token response, such as the user id, user name, role, etc.
  4. Implement the logic for the OAuth bearer authentication provider in a class that inherits from OAuthBearerAuthenticationProvider. This class handles the requests that contain the access token. You need to override the following methods:
    • RequestToken: This method extracts the access token from the request header or query string.
    • ValidateIdentity: This method validates the user identity and claims from the access token.
  5. Create a custom SSO provider that acts as a bridge between the two web applications. The custom SSO provider is a web API controller that exposes two endpoints:
    • /sso/signin: This endpoint receives a request from the first web application with the access token and redirects the user to the second web application with the access token as a query parameter.
    • /sso/validate: This endpoint receives a request from the second web application with the access token and validates the access token using the OAuth authorization server of the first web application. If the access token is valid, it signs in the user to the second web application using the OAuth bearer authentication middleware.
  6. Create an Angular service that handles the SSO logic in the front end. The Angular service should do the following:
    • Check if the user is already signed in to the current web application. If not, check if the access token is present in the query string. If yes, call the /sso/validate endpoint of the current web application and sign in the user. If not, redirect the user to the login page of the current web application.
    • After the user signs in to the current web application, check if the user wants to access the other web application. If yes, call the /sso/signin endpoint of the current web application with the access token and redirect the user to the other web application.

Frequently Asked Questions (FAQs)

Question: What are the benefits of using OWIN and ASP.NET Identity for SSO?

Answer: Some of the benefits are:

  • OWIN and ASP.NET Identity are open-source and well-supported by the .NET community.
  • OWIN and ASP.NET Identity provide a flexible and extensible framework for implementing various authentication and authorization scenarios.
  • OWIN and ASP.NET Identity use OAuth as the standard protocol for SSO, which is widely adopted and secure.

Question: What are the challenges of using OWIN and ASP.NET Identity for SSO?

Answer: Some of the challenges are:

  • OWIN and ASP.NET Identity require some configuration and coding to set up the OAuth components and the custom SSO provider.
  • OWIN and ASP.NET Identity do not provide a built-in UI for the login and consent pages. You need to create your own UI or use a third-party library.
  • OWIN and ASP.NET Identity do not support federated SSO with external identity providers, such as Google, Facebook, etc. You need to use a third-party service or library, such as Auth0, IdentityServer, etc.

Summary

In this article, you learned how to implement SSO with OWIN and ASP.NET Identity for two web apps using OAuth bearer tokens and Angular. You also learned how to create a custom SSO provider without using any third-party services.

Disclaimer: This article is for educational purposes only. The author is not responsible for any damages or losses caused by the use or misuse of the information or code provided in this article. The author does not endorse or guarantee the accuracy or reliability of any third-party services or libraries mentioned in this article. The user should always exercise caution and due diligence when using any online services or resources.