One of the projects on which we are working is a long-lived ASP.NET Web Forms system that is customized for a specific client. It is hosted by another company on a server which is external to the client’s environment and it does not have an access to the client’s internal network. The system is built by using the Form Authentication mechanism to authenticate and authorize the users. The list of users and their hashed passwords is stored into the database and the login functionality works in a classic manner – the credentials provided by the user on the login page are validated against the list of users in the database. If the provided credentials are valid then a new Forms Authentication session is established by calling the standard method FormsAuthentication.SetAuthCookie().
Recently, we had to extend that authentication mechanism by adding a single sign-on (SSO) capability which allows the client to integrate the ASP.NET web application with their internal Active Directory (AD) infrastructure. The requirement was to allow some internal employees to access the ASP.NET web application through SSO, but also keep the exiting database login functionality for the rest of the users who are external and they do not have internal AD accounts.
The ASP.NET web application is hosted on an external server and it does not have a direct access to the secured AD infrastructure. After doing some research, we found that in order to connect the external ASP.NET web application to the internal AD environment we can use a middle service called Security Token Service (STS).
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