Custom Basic Authentication for RESTful services

It’s very common when developing RESTful services to authenticate users against a proprietary user database. This is generally done with a combination of username and password through http basic authentication. Unfortunately, basic authentication is tied to windows accounts in IIS, which leads us to find out some alternatives or workarounds to support this scenario. WCF 3.5 made possible to authenticate transport credentials with one of the existing UsernamePasswordValidator extensions, however, this approach does not work for IIS hosted services.

Dominick solved this problem with a module plugged directly in the ASP.NET pipeline that works like a charm, but it requires some additional WCF settings and a custom IAuthorization policy to flow the user principal to the WCF service instance. His solution works for ASP.NET applications as well.

This problem can be also solved at a deeper level in the WCF transport model using a message interceptor. The message interceptor can receive a traditional Membership provider in the constructor class, and use it later for authenticating the users. In addition, this message interceptor can also automatically pass the user credentials to the WCF service instance.

As any other message interceptor, it can be configured directly in the WCF service factory with no need of having additional configuration. This can be easily done in the “svc” file hosted in IIS.

<%@ ServiceHost Language="C#" Debug="true" Service="Service" Factory="AppServiceHostFactory" %>

class AppServiceHostFactory : ServiceHostFactory

{

   protected override ServiceHost CreateServiceHost(Type serviceType, Uri[] baseAddresses)

   {

     WebServiceHost2 result = new WebServiceHost2(serviceType, true, baseAddresses);

     result.Interceptors.Add(new BasicAuthenticationInterceptor(

                System.Web.Security.Membership.Provider, "foo"));

     return result;

   }

}

BasicAuthenticationInterceptor is the message interceptor I built for this post, it receives the MembershipProvider and a default realm that will be returned together with an 401 http error (Unauthorized) in case the user was not correctly authenticated.

The example is available to download from here.

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