Active Federation using RIA Services and WIF

UPDATE: A coworker here at Microsoft has brought up some interesting thoughts regarding this approach, and I’ve added a brief discussion below the second diagram.

Recently I decided to experiment with RIA Services in federated authentication scenarios. For those of you that aren’t familiar with federation, let’s consider the following scenario: my company Contoso builds an expense reporting application that I host in the cloud. One day I get Fabrikam to sign up as a client, and now I have to onboard all Fabrikam employees onto my system. It is true that I could create a login for every employee, but that is impractical because Fabrikam employees have to remember that extra login, and also I would need to keep my list of logins in sync when employees join or leave Fabrikam.

The solution for this is federated authentication, where my app can use a third-party (Fabrikam’s) authentication provider (also known as a Security Token Service or STS) to authenticate users. I won’t try to explain federation from scratch, because Microsoft’s patterns & practices has a great write-up. You can squint and ignore some of the claims stuff as it’s not super relevant to what I’m describing here.

To build an app with federated auth using RIA Services, most folks resort to passive federation, which you might be familiar with from using things like your LiveID login. The passive approach is browser-friendly and uses a combination of cookies, URIs and redirects to log you in to the site you’re trying to access.  The downside in the case of Silverlight is that you cannot complete the login inside your app: you have to navigate away from the Silverlight control, type in your credentials into a HTML (or ASPX) page, and then be bounced back by your browser to reload the control. Another downside is that you need to host a HTML page for the user to type in their credentials, in addition to the Silverlight app and the web services, which might not be desirable.

The following diagram has a more detailed explanation of the exact flow that happens during the passive scenario:

From what I’ve seen, most folks use this passive pattern with RIA today. Eugenio Pace’s blog has a few great write-ups and demos that you can try out. Some are a bit dated, but you should be able to find your way around.

What I wanted to try out was the active federation case, in which the Silverlight app talks dirctly to the identity provider. This has the benefit of having the user type their credentials directly into the Silverlight app, without having to leave the page, which results in a more polished and faster user experience. Eventually, as the crypto support in Silverlight improves, it may end up being a more secure solution as well, if we are able to encrypt and sign the tokens that are being exchanged. The following diagram demonstrates the slightly different message flow in the active case. Note that the app itself is doing most of the work, not the browser.

Some interesting considerations emerged in conversation with Robert O’Brien, an architect here at Microsoft. Please consider these before building your own app:

• One of the things we gain in this approach over a passive federation approach is the ability to log the user in from inside our UI. That provides for a better user experience, but it also puts the burden on our app to expose a credentials UI and pass the token over to the service. Potentially this could be a security risk for our app. Some folks believe that this goes against the spirit of federated authentication since it takes control away from the identity provider.
• The implementation shown here relies on WS-Trust as the protocol for the token. Unfortunately in today’s federated web, it seems like only ADFS and maybe OpenID servers honor that protocol. If you are trying to use WS-Trust and use Facebook/Yahoo/Google (either directly or through Azure’s Access Control Service) as the identity provider, you will find that WS-Trust is probably not supported. So outside the enterprise environment, this approach might not work.

Now some specifics of the sample. It’s a simple master/detail application that allows you to display and edit data. There are two registered users fabrikam\yavor and fabrikam\test and the password for both of them is 12345. If you don’t log in and try to display the data, you will get an error because of the EnableClientAccess attribute.

[RequiresAuthentication]
[EnableClientAccess()]
public class CustomersService : LinqToEntitiesDomainService<AdventureWorksLT2008R2Entities>

All authenticated users can view the data, but only users in the Editor role can make changes to it. Only the user fabrikam\yavor is in that role.

[RequiresRole("Editors")]
public void UpdateCustomer(Customer currentCustomer)

The bottom line here is that even though we have a STS with external user authentication, we kept authorization local to our app (we use ASP.NET roles). That’s a choice you can make as a developer - you can also externalize the user roles (or claims) as part of the STS, or keep them local.

There are lots of extra details in the app, which you’ll see by exploring the source.

The code is available here. Note that you need the following installed on your machine for it to work:

• Visual Studio 2010
• SQL Server 2008 R2 Express
• SQL Server 2008 R2 Management Studio Express 
• WCF RIA Services V1 SP1/SP2
• Windows Identity Foundation Runtime
• The AdventureWorks LT 2008R2 database for SQL Server Express 2008 R2

Here are some additional notes on the structure of the sample:

• First, please run the included SetupCertificates.cmd script inside the Scripts folder
• The solution will create two applications in your local IIS instance: AddressBookFederatedAuth and IdentityProviderAndSts. Make sure you launch Visual Studio as Administrator, so it has permission to create those. Also make sure you enable HTTPS so both of the applications in the IIS Manager
• Change the Application pool under which those applications are running to use the Network Service account. 
• Use SQL Server Management Studio, make sure Network Service is added as a login to your SQL instance. When you add the account, make sure you give him some sane Server Roles (for example sysadmin). Let me know in the comments if you find any of these steps difficult and I can provide more detailed instructions.

I want to credit Eugenio Pace, Kyle McClellan, and the folks behind the Identity Developer Training Kit, from where I shamelessly stole some code.

RIA Services T4 template to copy comments from server to client

As you know one of the new features in RIA Services V1 SP1 is support for T4 templates. The T4 template is a design-time artifact that can modify the way RIA Services client-side code generation happens. For more information on T4 templates, check out Jeff Handley’s blog post on the subject.

Recently I was experimenting with RIA Services and I discovered that the IntelliSense comments for my entities were very sparse on the client. For example my Customer entity has a CompanyName property and the IntelliSense comment for that was:

Gets or sets the ‘CompanyName’ value. 

It was clear that this comment was being generated automatically, which was quite annoying because I had used my entity model on the server to carefully create useful comments for each property.

I hear EF is actually smart enough that it supports defining these comments in the database itself, and they will get copied over when you create the model, but I haven’t tried it myself.

So I set out to write a T4 template to take those comments from the server types generated by EF and copy them over to my Silverlight project.

The first step was to tell Visual Studio to scrape all the types in my server project and generate a XML file containing their comments, by going to the Build tab of project properties and checking this box: 

This file is usually used for IntelliSense, but you can open it up and the schema is pretty self-explanatory. Because code comments don’t get compiled into assemblies, this is the only way I know to tell VS to export the comments from my entities.

The next step was to write a simple T4 template using RIA Services extensibility. What this does is that as it is about to generate a type on the client (which happens when you build), it will look up that type name and all its properties in the above XML file, and copy the comments over to the generated file.

[DomainServiceClientCodeGenerator(typeof(CommentsClientCodeGenerator), "C#")]
public class CommentsClientCodeGenerator : CSharpClientCodeGenerator
{
    private XElement comments;

    public CommentsClientCodeGenerator()
    {
        comments = XElement.Load(new FileStream("..\\AddressBook.Web\\bin\\AddressBook.Web.XML", FileMode.Open));
    }

    protected override EntityGenerator EntityGenerator
    {
        get
        {
            return new CommentEntityGenerator(comments);
        }
    }

    public class CommentEntityGenerator : CSharpEntityGenerator
    {
        private XElement comments;

        public CommentEntityGenerator(XElement comments)
        {
            this.comments = comments;
        }

        private string PrintInnerXml(XElement element)
        {
            string[] lines = element.Nodes()
                .Aggregate("", (b, node) => b += node.ToString())
                .Split(new string[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries);
            StringBuilder sb = new StringBuilder();
            foreach(string line in lines)
            {
                sb.AppendLine(line.Trim().Insert(0, "///"));
            }
            return sb.ToString().Trim();
        }

        private XElement FindCommentElementByName(string name)
        {
            return comments
                .Descendants("member")
                .Where(x => String.Compare(x.Attributes("name").FirstOrDefault().Value.ToString(), name, true) == 0)
                .FirstOrDefault();
        }

        protected override void GenerateClassDeclaration()
        {
            XElement element = FindCommentElementByName("T:" + this.Type.FullName);
            if (element != null)
            {
                this.WriteLine(PrintInnerXml(element));
            }
            base.GenerateClassDeclaration();
        }

        protected override void GenerateProperty(PropertyDescriptor propertyDescriptor)
        {
            XElement element = FindCommentElementByName("P:" + propertyDescriptor.ComponentType.FullName + "." + propertyDescriptor.Name);
            if (element != null)
            {
                this.WriteLine(PrintInnerXml(element));
            }
            base.GenerateProperty(propertyDescriptor);
        }
    }
}

That’s all I had to do… as soon as I started building this class (in its own project) inside my solution, the code comments I defined on the server started appearing in my Silverlight client.

The code is available here. Note that you need the following installed on your machine for this to work:

• Visual Studio 2010
• WCF RIA Services V1 SP1
• WCF RIA Services Tookit December 2010
• The AdventureWorks LT database for SQL Server Express 2008 R2. You only need this if you want to actually run the sample.

Hope you find this useful!

Презентацията ми за WCF и Silverlight от Дни на Microsoft ‘11

Ето и презентацията ми за Silverlight и WCF услуги в Windows Azure. Очаквайте и демонстрациите скоро! Отдолу ще намерите презентацията и примерите които показах.

Примери

• Използване на WCF NetTcp услуги в Azure от Silverlight
• Федеративна сигурност с WCF и WIF

Презентацията ми за WCF RIA Servces от Дни на Microsoft ‘11

Благодаря на всички които дойдоха на моята презентация за RIA Services миналата седмица по време на Дни на Microsoft ‘11. Отдолу ще намерите презентацията и примерите които показах.

Примери

• T4 templates за копиране на описания от сървърския RIA Services проект в Silverlight проекта
• Федеративна сигурност с RIA Services и WIF

Accessing SharePoint UserProfileService from Windows Phone 7

UPDATE: … and it wasn’t long before Matthew McDermott went ahead and implemented ths as an actual sample, which you can get here.

A while back I blogged a workaroundfor accessing some ASMX services from Silverlight 4. The problem was that the guid and char types that those services return are not recognized by Silverlight and you end up with the exception below. One of the important services affected by this is SharePoint’s UserProfileService, which I realize is pretty important to a lot of developers.

System.ServiceModel.Dispatcher.NetDispatcherFaultException was unhandled by user code. The formatter threw an exception while trying to deserialize the message: There was an error while trying to deserialize parameter http://tempuri.org/:HelloWorldResponse. The InnerException message was ‘Error in line 1 position 268. Element ‘http://tempuri.org/:HelloWorldResult’ contains data of the ‘http://microsoft.com/wsdl/types/:guid’data contract. The deserializer has no knowledge of any type that maps to this contract. Add the type corresponding to ‘guid’ to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding it to the list of known types passed to DataContractSerializer.’.  Please see InnerException for more details.

(Same goes for http://microsoft.com/wsdl/types/:char)

We have already fixed this issue and you will not need the workaround anymore in the next version of Silverlight.

In implementing the workaround, I used an IClientMessageInspector, which unfortunately is only available starting in Silverlight 4. So all of our developers using Silverlight 3 (and in particular folks writing apps for Windows Phone 7) cannot use the workaround.

Fortunately, there is a way to “fake” an IClientMessageInspector on older versions of Silverlight, and I wrote a sample for that back in the Silverlight 2 days. So combining these two samples together, you can be on your way:

1. Create a “fake” IClientMessageInspector like in this sample
2. Use the IClientMessageInspector implementation that treats the guid and char types emitted by ASMX from this sample.

Hopefully this will unblock folks out there, if there is significant interest here I can create a combined sample that shows the whole thing end-to-end.